One afternoon in London

Traffic in central London is heavy, and HO/HO buses have to stop to let people off and on, so I wouldn't choose a HO/HO bus as a familiarization tool. If you must travel around by bus, I'd recommend a bus tour of some sort. That's got to be a bit more efficient than a HO/HO bus.

But have you been to Europe before? Are you certain you won't have a significant jetlag problem and will be reasonably awake after an overnight flight? Most people are affected to some degree by jetlag, and the usual suggestion is to walk around outdoors to try to get you body into the right time zone. Some travelers are so sleepy they are virtually zombies. I know that if I sat down on a bus on my arrival day, I would be asleep within 5 minutes, so any kind of bus tour would amount to an expensive nap for me.

If you're alert enough to function, I'd recommend taking one or two of the walking tours offered by London Walks. They cost only 10 pounds and you needn't make a reservation. You can just show up at the meeting place if the weather and your energy level are conducive to taking a guided walk.

I'm sure one or more of our London experts will be along within a day or so to suggest a self-guided walk.

Thank you for the suggestion. I will definitely
look into walking trips. This is my first international trip. My partner lived in Germany for a few years in the early 90's, so he's a tiny bit more ahead of the curve than I am. He also warned me about the possibility of jetlag. I planned to take a couple of melatonin on the plane and sleep as much as possible. I'm one of those rare people who can survive on very little sleep (4-6 hours on a good night). My partner on the other hand requires significantly more sleep than I do. He knows I'm not opposed to a little solo adventuring if he needs a bit more rest.

Here she comes again with another post about boats:

London has a system of "river buses" that enable you to see the sites along the Thames. Each boat has a snack bar for light fare and beverages. I seem to remember some commentary too.

https://tfl.gov.uk/modes/river/

Thank you for the suggestion Marty! I hadn't thought of river busses, I'll look into it as well!

When is this trip?

When you say your hotel is near Heathrow how close are you? Walking distance? Cab ride? Bus?

I’m asking because here’s a plan to consider:

Use the 15 minute Heathrow Express train from Heathrow into Paddington Station. At Paddington use a debit or credit card to get each of you your Oyster card. If you didn’t use an ATM near your accommodation to get pounds from Paddington Station walk over to the Pride of Paddington Pub. There’s an adjacent Barclays Bank ATM. Get about 30£ Each and then walk (about 8 blocks) over to and into Hyde Park via the gate off of Bayswater road at the Italian Gardens. Well signed paths will take you into Kensington Gardens where you can see Kensington Palace.

From there walk over to the Albert Memorial and Royal Albert Hall. Head to the V & A museum to have a pleasant late lunch at their cafe. OR if seeking a pub to have lunch at try the small Queens Arms pub in the Queens Gate mews.

Sated walk to the Knightsbridge Tube Station. Use the pounds you got to put money on your Oyster card ( 10£’s on each should do) .

Then for your first tube ride take the Piccadilly Line
( Dark Blue on the map) 2 stops to South Kensington. Exit the train and then take a District ( Dark Green ) or Circle Line ( Yellow) to Westminster. Don’t be overwhelmed by the tube. Large maps on the wall and signboards over head, as well as attendants to ask. Honestly it’s a breeze when you know where you are going to.

When you arrive at Westminster walk out to Parliament Square. Even though Elizabeth’s Tower with the Big Ben bell is in scaffolding you will enjoy recognizing Parliament and nearby Westminster Abbey. After photo ops walk up Birdcage Walk
( again well signed) into St James Park and onto Buckingham Palace. If the flag is atop the Palace it means the Queen is in residence.

Depending on your stamina you could walk past the Palace and the Victoria Memorial into and through Green Park to Piccadilly or head back the way you came.

Edited: and DONT bother with the Hop On Hop Off bus. With London traffic waste of time and money!

I once took a coworker on a whirlwind tour of the city using the underground. While we didn’t have time to go into anything he at least got to see the main sights, Westminster Abbey, Parliament and Big Ben, Tower of London and Tower Bridge, Buckingham Palace, and Monument. We also stopped at Black Friars for a drink. Had we not had to meet up with other coworkers we would have walked from 10 Downing Street over to Trafalgar Square. In the evening we went to the Blackbird Pub by Earls Court tube stop.