this is my suggestion for the London tour.
At Paddington, we take the tube to Victoria.
From there, we'll walk to Buckingham Palace, and if it's not too busy (which it will probably be), we might be lucky enough to see the Change of the Guards at 11.30.
Afterwards, we walk up the Mall to Trafalgar Square and take a look around.
Then, it will probably be time for lunch. There are a good number of lunch places on the Strand, from sushi at itsu to sandwiches at Prêt and the best (but, alas, not cheapest) hamburgers in the world at Byron. We could split up as we probably can't make everyone happy, and meet again later.
After lunch, we walk towards the river to Westminster to see the Houses of Parliament (or how a dad I overheard there put it: "where all the mp's sit and shout at each other") and Big Ben. We'll cross the river and walk past the Big Wheel to Waterloo, where we take the tube to Soho to go crazy in the Forbidden Planet. To top it all off, we'll take another train to Westfields Shepherd's Bush, brave the shoppers and finish our tour at one of the London LEGO stores.
From there it's only a short tube journey back to Paddington, where we take the train back to Slough at about 5 pm.
Now, fortunately the strike was called off, so I'll give you a convenient train time soon. We'll hopefully be on that train, coming from Reading, and will meet you at Paddington.
Of course, this itinerary is only one option - the one I am going to go with. It's perfectly fine for anyone to do their own thing and meet us at one of the landmarks, or even back at Paddington or Slough, if you know your way around trains. :)
When you buy your train ticket, you should not take the cheaper off-peak ticket, as you can't take any train for the way back with it and might have to wait until it becomes valid.
But do make sure you go for the Travelcard option when booking the tickets - we need zones 1-2, but there might only be the zone 1-6 option, which is fine, too.