St.Pancras International to Hop On Hop Off location

I'd do either a Black Cab to Marble Arch, which has the most bus routes, basically you ask for 'Speakers Corner', that would cost around £13-15.

Or, the Tube, which is super easy, from King's Cross (next to St. Pancras, just cross the street) to Green Park, using the Victoria Line (light blue) or Piccadilly Line (dark blue). The tour buses stop by The Ritz Hotel, right next to the station. 1-2 people, the Tube might be cheaper, 3+, the cab is probably cheaper.

Walking is definitely an option, you can pick up the Blue Bus Line (T4) from Russell Square, which is less than a mile away, maybe a 20min walk if not rushing. There is a Tube stop there also, but likely to be the same price to go to Green Park, where there are more routes available.

Is this a day trip from Paris?

What time is your train back?

Thanks for your reply!
Do you know, do the Black Cabs accommodate 4 adults?
And I assume they are plentiful to hail outside St. Pancras? ... we're thinking the Black cab would be a good option. ( Boy, the tube single journey tickets are expensive!)

Nigel, we are travelling from Brussels and returning to Brussels that evening. ... a whirl wind tour of London!

Our return train leaves at 7pm.

I would follow Mike J's suggestion and just walk from the station to the stop at Russell Square/Wolburn Place. Twenty minute walk. Then you can get on the blue line Museum Tour bus, take it to the Ritz Hotel, disembark, and wait for the yellow line Original Tour bus.

The ticket is good across tours according to the website. Save money on the cab and the underground. Walk!

Make sure you don't cut the Eurostar check in too fine. Both in Brussels and in London, Eurostar have very strict 30 minute cutoffs at the check in desk. After you check in you still have to go through security and border control.

Queues can build up. My current suggestion is to be there between 50 minutes and an hour ahead of departure time.

Since in order to be on the 1904 to Brussels it must be a weekend, I'd advise to check the TfL website to see what bus and tube lines will be closed during your visit.

Yes, 4 people fit comfortably in a black cab, two facing forward on the seat and two facing backwards on the little pop down seats.

With 4 (all adults?) cabs can begin to make sense. Think Tube prices are high (where are you looking?) wait till you see how expensive the rest of London is - black cabs included. How much are those 4 seats on the HoHo going to cost you?

Is the HoHo the best use of your money and time. My experience is that they are ok (ish) if you stay on, but sometimes a long wait to get back on.

Tube fares are super pricey if you're not using an Oyster Card, especially in Zone 1. If you have a 'Contactless' credit or debit card, it can be used as an Oyster Card also, fare pricing is the same (greatly reduced from cash fares and capped at £6.80 a day I think) and you don't have to add credit to the card, or pay £3 for the card itself. You would each need one though.

There will be plenty of Black Cabs available at St. Pancras, they take up to 5 people.

A one day trip from Brussels, that really is a tough one, a long way to come for a few hours. I've driven from London to Brussels and stayed over night, and I was so tired. LOVE Belgium by the way, if they ever kick me out of London, I'd move to Belgium... big beer fan!

Have a back up plan for if it's raining, which it could easily be, as the tour bus experience really only works on a sunny day, on the open top deck. The British Museum is walkable from St. Pancras.

As the saying goes "It doesn't rain all the time, but it could rain at ANY time".

HoHo buses can give you an overview of many cities, but they struggle in London as there is too much for a single route to handle - indeed the 'Official' tour run three interlocking ones, and I'm not sure if you can comfortably do all three. They are also priced really to be cost effective for two days, meaning you are in a way paying double.

As an alternative are there anything you really want to go to? Two or three could easily be visited, taking cabs in between for the 4 of you.

Or put together your own tour using the regular scenic bus routes suggested on here an elsewhere. That would be £5 each for a one day bus and tram pass, which you can by at St Pancras, probably easier than dealing with Oyster cards for one day. If you end up a long way away take a cab back in plenty of time ...

Also, consider traffic during weekdays. If touring during the week, you could spend a lot of time in local traffic. Roads are pretty clear in Central London over the weekend, especially before midday, assuming there isn't some huge event on and they close all the roads, which they have done today.

Not trying to be the voice of doom, but would hate it if you made the effort to visit, and didn't enjoy it :o(

This is just a day trip, travelling from Brussels to London and back again that evening ... we had an extra day in our trip and thought, what the heck, let's "see London".
It is perhaps a very "touristy" thing to do but, given none of us (yes 4 adults) have ever been to London before, and knowing we really don't have time to tour any specific sight extensively, we thought it would be nice to just "see" many of the major sights - hence, the choice of the Hop On Hop Off. And, if we can grab some quintessential "fish and chips" for lunch, perfect.
Thanks everyone for your thoughts. And if anyone has anymore tips, I would welcome them. And here's hoping for a sunny dry day! :-)

Just want to tag this one so I can find it again.

Here's my suggestion for your quick trip. Traffic is London is like any big city, moves at a snails pace. Better option in my humble opinion is cough up the money for your 1 day tube excursion. From St Pancras ride it to Westminster Station. I think the Victoria line from St Pancras is your best option changing once to get either a District or Circle train to Westminster but I could be wrong so definitely ask. OR hopefully a Londoner will provide the correct means to accomplish this tube excursion. The big map on the wall of the tube lines is very helpful in figuring out your route as well. Once at Westminster, exit to visit Parliament Square which includes the iconic Parliament building, Big Ben and nearby Westminster Abbey. You are also near the Thames and can see the London Eye from Westminster bridge. Depending on your preferences you could walk up Birdcage Walk thru St James Park and over to see Buckingham Palace. From there walk thru Green Park to Piccadilly and walk to Piccadilly Circus. Or if seeing the Palace isn't high on the list , from Parliament Square stroll up WhiteHall to Trafalgar Square. You'll pass 10 Downing street (which you can't see) and the Horse Guards which you can see. Fish and chips at the Red Lion Pub in route isn't bad. Eaten it more than once. Or from Trafalgar Square walk over to Covent Garden and try this place for your fish and chips. rockandsoleplaice.com. Google a bird's eye view of London and pinpoint where things that interest you are located. Look for the red circle icons with the horizontal blue line thru it. Those are tube stops. Have a wonderful, short, quick visit.

Thank you Claudia!

Just found out that our one day in London coincides with the Gay Pride Parade, meaning closed roads, slow traffic, altered bus (city and HOHO) routes .😕
Does anyone think a black cab tour would be ok ( hopefully they could skirt around closed roads, etc) or should we brave the tube? although I hate the thought of travelling underground)

With a short time, I would look at taking Rick Steves Audio Walking Tours ,here . Just follow along and enjoy the city. Find a great pub, enjoy lunch, walk along the Thames. I did the HOHO Bus last time I was in London. Traffic was terrible! We finally just got off and walked! I would definitely follow RS walking tour and enjoy! Here's the map.here