12 hour layover in London

Is 12 hours the difference between your scheduled landing time and scheduled takeoff time?

For a flight to Africa you’re recommended to get to the airport 3 hours before takeoff time. You’ll have to clear immigration and customs on arrival and departure (and security on departure too) - immigration on landing will probably be the slowest part. Will your hold baggage be checked through to your final destination, if so this will make it much quicker to exit the airport.

Best way to London is probably the Elizabeth line on the underground (subway) system. I don’t know about HoHo buses- they seem very expensive to me. I don’t think you can book anything in advance in case the incoming flight is delayed.

Personally I would avoid the HoHo buses like the plague unless you like sitting in traffic.

How about Piccadilly Line (tube) to Hammersmith, cross the platform and board a District Line train to Westminster. Emerge under the Elizabeth Tower, see Parliament and the Abbey. Walk over Westminster Bridge ( do not engage with hawkers and do not accept any heather) or the Golden Jubilee Bridge and have lunch on the South Bank. Then walk East along the river to Tower Bridge and cross to see the outside of the Tower. Then make your way to the Elizabeth Line and straight back to LHR.

But what is happening to your bags?

Many factors will affect timing, including flight arrival time (if it is on time) and the day of the week. You will likely not have a full 12 hours, as you need to get through immigration, find somewhere to store your carry on bags, freshen up, procure tickets to transportation choice, take transit to London (45-60 minutes depending on time of day), find something to eat, spend 45-60 minutes getting back to the airport and arriving there at least three hours ahead because you need to get your stored bags, ensure you're checked in for Africa flight, and get back through security (can be very slow). You may also switch terminals from arrival to your onward flight, so pay close attention as you don't want to store carry on bags in an inconvenient location.

10 people is a lot of people to coordinate, especially if you're arriving during a peak travel time (rush hour, busy weekend). Also if you're getting off an overnight flight, jet lag + HOHO bus is a recipe for sleeping in London traffic. I've done it myself, do not recommend. Search this site for recommendations for alternatives to spend a long layover. Something easier and closer to the airport may be less stressful for all.

Here's the official London journey planner for public transit if you decide to go that route. You'll need to figure out fares too or make sure each individual has a contactless credit card to pay for the tube (no point in buying Oyster cards for such a short visit)
https://tfl.gov.uk/plan-a-journey/

The most cost effective way for a group of ten people or more from Heathrow to Central London then all day travel is not credit cards or Oyster. If your travel is going to start after 9.30am Monday to Friday, anytime at weekends you can buy a group day travelcard for £10.50 each at Heathrow, from the ticket machines. (£5.20 for anyone under 16)-
https://tfl.gov.uk/fares/find-fares/tube-and-rail-fares.

That is £5 less each than the equivalent daily cap paying by any other method,

The devil is in the detail here. What are the times of your arrival and departure?

You can expect to take about an hour to get through the airport and another hour to get into London. You will have to clear customs but that will take seconds. It’s immigration that could take time although normally it’s OK.

Then an hour back and the airline will almost certainly advise arrival back at LHR 3 hours before departure. Assuming your flights are on one ticket any checked bags should stay at the airport so you could maybe shave a little time off that as all you will need to do is clear security again. So your 12 hours will shrink to 6 actually in central London.

HoHo tours are an excellent way to see many cities but not London. The traffic is horrendous so the buses make slow progress, they are not allowed to visit some areas like Buckingham Palace and it can often be difficult to get back on them if you get off. And presumably coming off a red-eye flight, there is a high danger of you falling asleep on the bus. Much better to be out in the fresh air.

I would do as camborne2018 suggests - that’s an excellent plan which should work assuming your flight in is on time.

An alternate suggestion is to visit Windsor and tour the castle. Stop in a pub for a meal or a drink.

With ten, I suggest you hire a car service to take you to Windsor and then drive you back to the airport.

What airline are you flying? Exactly what is your flight schedule? Are flying on one ticket?

Departing LHR is the same as the USA. You will go through security and on to your gate, there is no passport control for departures,

Can I suggest a modification to Camborne 2018's itinerary (based on the premise that you will only have small hand baggage with you that you are happy to carry around:

Get the Piccadilly Line/District lines (as Camborne 2018's idea) but get off one stop before Westminster at St james's Park. Walk the short distance into the park itself and see Buckingham Palace framed above the lake etc. From there walk to Parliament Square (where Westminster Station is) and look at the sights around Westminster and the north side of Westminster Bridge etc as per Camborne 2018's post.

Then, instead of crossing Westminster Bridge, get a number 26 bus from the bottom of Whitehall which will probably show the destination 'Bow Church' (and not Victoria which is the wrong way). This will take you past a number of the main tourist sights.. Go upstairs - the best views will be from the front seats but there's only 4 of them and 10 of you. For the others the best views will be from the left hand side of the bus. It goes past Downing Street (not much to see due to the security gates), Trafalgar Sq, down the Strand and Fleet St (past the magic castle-looking Royal Courts) and around St Paul's Cathedral. You then go past the Bank of England and Royal Exchange and then get off at Liverpool St station and get the Elizabeth Line back to LHR. There are plenty of YouTube videos about how to take buses, pay for them etc.but in short use the same card each that you used to get to St James's Park.

Other than The Tower, you will have seen most of the major sights and for a fraction of the price. You can, of course, hop off the bus and hop on the next one. There's one about every 8 mins.

Good luck!!

A bus on Route 26 will have a destination of Hackney Wick, not Bow Church

If you are travelling on the cost effective paper Group Travel card just one person shows that to the driver, you don't tap it anywhere on a bus or train. Quick and easy boarding process.

To answer your question: Yes, it is possible to take the HoHo bus with that layover. At one time you could buy the tickets in the buses at any stop. Not sure if that is still possible as it has been some years since my first trip to London, when I made use of this service. You can also buy tickets online if you are comfortable with that. Yes, there is traffic, but you don’t see much from the tube, so there is that.

A few years ago, I had a similar layover on my way to Cape Town and took the tube to Kew Gardens and then had a nice late lunch at a French restaurant in Kew before heading back to Heathrow. You can transfer at Hammersmith from the Piccadilly to the District Line. Only state this as an example of what is possible.

If you want to take the HOHO bus, this company has a ”red” and ”blue” route and both stop at the Green Park Underground station which is on the Piccadilly line. Take the tube from Heathrow to Green Park. There are no changes. It will take you about an hour to get from Heathrow to Green Park.

I am not a fan of HOHO buses (YMMV). As an alternate suggestion, you could walk along the south bank of Thames where you would see the Houses of Parliament and great views of other London landmarks like St Paul’s dome and the Tower bridge. If you wanted to do this, take the tube to Hammersmith. At Hammersmith, change to a District line train on the opposite side of the platform and take the train to Embankment. At Embankment, exit towards the river and cross the river using the Golden Jubilee pedestrian bridge. From there, you can walk along the path.

You will probably have about 6 to 7 hours to explore London on a 12 hour layover. Allow about an hour on arrival to get from your gate to the tube station and then another hour to get to London. If the egates are working, you should get through faster; on arrival, you go through immigration and customs. You will need to arrive at the airport about 3 hours before your flight departs. You will go through security. Pay attention to what terminal your departing flight leaves from. You can take the Piccadilly line back to Heathrow and you will need to leave London about 4 hours before your flight; pay attention to the Heathrow terminals the departing trains stop at and make sure to take a train that stops at the terminal you need.

The Elizabeth line is faster to London but it doesn’t stop particularly close to any tourist sites. I think the tube will be better for the HOHO bus,

CORRECTION: I see the blue route of the big bus stops at Paddington. So you could take the Elizabeth line to Paddington and join the HOHO bus there:
https://www.bigbustours.com/en/london/blue-route-london

There's also Golden Tours - https://www.goldentours.com/london-hop-on-hop-off-bus-tours

and TootBus - https://www.tootbus.com/en/london/home

I don't think the traffic is as bad as people make out. Maybe I'm just used to it and I never drive in central London. Traffic is noticeably lighter than it was a few years ago. I looked it up and traffic in central London in 2022 (the newest figures I can see) was down 14% on 2019. Might have still been post-pandemic, but my personal perception is that it's not as bad as it was. source

Roads are probably quietest from about 9:30am until midday or 1pm. I'm not sure which day the OP is coming in, but in general I think a HoHo bus would work fine on a Saturday morning or most of the day Sunday particularly.

they are not allowed to visit some areas like Buckingham Palace and it can often be difficult to get back on them if you get off. And presumably coming off a red-eye flight, there is a high danger of you falling asleep on the bus. Much better to be out in the fresh air.

Nor do ordinary London buses pass outside Buckingham Palace. But the HoHo buses, like the red London buses, do stop literally round the corner, in Buckingham Gate, opposite the King's Gallery.

Most of the HoHo buses are open top, so you are out in the fresh air.

There is also the ubiquitous City Sightseeing- https://city-sightseeing.com/en/95/london

An alternate suggestion is to visit Windsor and tour the castle. Stop
in a pub for a meal or a drink.

With ten, I suggest you hire a car service to take you to Windsor and
then drive you back to the airport.

I second Frank II's suggestion. We did exactly this a few months ago, substituting Uber for the car service. (And we were staying overnight at Heathrow so did not have to deal with luggage.)

At any rate -- Windsor is a charming little town. If you are lucky to have a sunny day (like we did) you can stretch your legs on the Long Walk. We had delicious Fish & Chips at the Duchess of Cambridge, just across from the castle. It was a very enjoyable, stress free day and a nice mid-trip break.