Half Day in London

From Paddington Station use the Underground. Use a tap credit or debit card and either board a Circle Line train ( yellow on the map ) or a Bakerloo Line train ( brown on the map) for direct (no changes) access to Westminster station. Walk out side and you’ll be in the shadow of Elizabeth’s Tower. If you exit on the hour you’ll hear Big Ben toll. You are at the most iconic part of London, Parliament Square.

From there you could:
Follow Birdcage Walk through St James Park to the Palace. If the Royal Standard is flying then King Charles is in residence OR take a tour of Westminster Abbey OR walk across Westminster Bridge ( paying no attention to the countless shell games and making certain your purse, backpack, wallet is secure). Or your could take a River Sightseeing cruise to the Tower of London and back.

However you made mention of Harrod’s so I’ll
surmise you’d like to see it….as far being the main one, there’s only one Harrods. It’s on Brompton Road in the Knightsbridge neighborhood. If that’s your preference then at Paddington you can take various tube lines to get there. Use the https://tfl.gov.uk/ to plan your route.

As far as Good Omens London filming locations; there’s the Sky Garden ( Heaven’s top
Floor), St James Park, Battersea Bandstand in Battersea Park.

I wouldn't attempt the British Museum unless you want to pre-book admission for a specific time; I assume that would speed up entry through the security line (typically 30 minutes or so, in my experience). Actually, for a very quick stop in London like this, I wouldn't go to the British Museum even with a prebooked ticket, because the museum is usually really, really crowded, and it's large, so you can't see things quickly. Better to use your time elsewhere.

The National Gallery is also large, but I've never run into a significant delay at the entry, and there aren't usually crowds except around a few very famous paintings.

Among the smaller museums not in obscure, hard-to-reach locations are the Courtauld Gallery and Sir John Soane's Museum. Both of those are sort of between the British Museum and the river, to give you an idea of the geography.

But if you have nice weather, I prefer Claudia's idea to spending the time indoors at a museum.

You don't have as much time to see inside locations as you think you do. Many don't open until 10 am and then you have to be out of there by noon. I would suggest spending the first part of the morning walking around and enjoying sites. Then pick one location to spend your last 2 hours. What interests you the most?

I think Acraven and Carol are right that I don't have time for a museum. I think having a place to go as a back up if the weather is bad would be great. Carol you asked what interested me the most and I will say easy. This is our last day, we will be stressed for flying out and everything.

Maybe grab our breakfast sandwiches from the Train Lounge and walk through Hyde Park (setting of so many romance novels) to St. James Park. Do the Birdcage Walk, then feed the ducks. Do they have little machines to buy duck food? Maybe have an ice cream at Berkeley Square? Is there any good window shopping? Is Harrods a bad idea? Are there good markets to wander through and get a bit to eat? Can you wonder through the lobby of the Ritz just to see what it looks like?

You could walk from Paddington Station to Bayswater Road (8 minute walk) when you get there cross the street and enter Hyde Park. Walk through Hyde Park to Harrods (10 minute walk). When you enter Hyde Park you’ll see the Italian Gardens, after a short walk you will come to Lido Cafe where you can have some tea or anything, then finish walking to Harrods. The food halls are fabulous, so much fun to see. A person could spends hours in Harrods just looking. They have a Harrods department full of gift items that is fun to look at and to purchase a few things. By that time it would be time to walk back to Paddington Station to go to Heathrow.