Pre Purchasing Tickets

Pre-book:

1. Buckingham Palace if it’s open when you’re here.
2. Churchill War Rooms (suddenly ultra-popular since The Darkest Hour)
3. Harry Potter studios if that’s your bag
4. Train tickets for certain destinations (Bath & York both have big reductions if you book in advance but I don’t thinkOxford or Bletchley Park do.

The other thing you might want to book is a special art exhibition. The major galleries & museums (National Gallery, British Museum, V&A, both Tates etc) are free to enter but you need to pay for special exhibitions and some may need pre-booking.

In September no need to prebook. Crowds will exist but not the huge Summer hordes.

Remember to research the Days Out 2 for 1 deals. Could save you money at Westminster Abbey and Tower of London.

I too love walking. London is a walkable city. You’ll thoroughly enjoy walking in Hyde Park and Kensington Gardens.

Walking along Regents canal is also enjoyable.

Or do the wee climb up to Primrose Hill in Regents Park.

There’s also the Thames River path.

Hidden gems?

Check out what’s on at the Wilton Music Hall. Or Royal Albert Hall.

Don’t pass up Portobello, Brick Lane and Camden Lock Markets.

If you like intriguing old cemeteries then pre book a tour of Highgate where Karl Marx is buried.

Try evensong at St Brides then meander the streets and alleys on the City of London. Pretty much untouched for centuries.

Enjoy a respite at the stunning Art Deco adorned Blackfrairs pub.

10 days is a near perfect amount of time. You’ll see a lot but not all of what this great city offers.

Enjoy.

I'd probably book the Houses of Parliament tour in advance if that is of interest, although it usually isn't necessary.

I'd suggest looking into London Walks. For ten pounds per person, you get an excellent two hour guided walking tour and they have just about any theme you can imagine. http://www.walks.com/

Unusually for a close-to-London destination, it is worth buying Advance tickets to Oxford for specific trains from either Marylebone or Paddington. Costs start from around £5, depending on whether there is a sale on. Journey time is roughly equivalent on the express services.

Many London attractions are now a few pounds cheaper if booked in advance online. Some examples I found in my (non-comprehensive) research:

Churchill War Rooms £18.90 online / £21 in person
St. Paul's Cathedral £16 online / £18 in person
Royal Observatory Greenwich & Cutty Sark combo-ticket £15.65 online / £20 in person
Westminster Abbey £20 online / £22 in person
Tower of London £22.70 online / £26.80 in person
London Transport Museum £16 online / £17.50 in person
Kew Gardens £16 online / £17 in person

And yes, the Churchill War Rooms are indeed very popular now, so pre-booking a timed admission is worth it to get in the shorter line, as well as to save some money. They are so busy that even some people with timed advance tickets had to wait a bit - but not as much as those of us (myself included) who did not have advance tickets.

Regarding those 2-for-1 deals, do you really have to have a rail ticket for that day? I got all excited, adding all sorts of places to my cart, then saw the rail requirement. We will be arriving in London via train from Oxford, but not on the days we want to see the other sights. Hadn't heard of this deal until reading this thread.

Since the offer is promoted by the train operating companies you most certainly need rail tickets that encompass the days that you visit the attraction (there are offers nationwide, although most discussion on here relates to London).

Your single ticket from Oxford would cover you in London on the day. If you are going in to somewhere else after London the pair would do. Otherwise you need to buy your around London travel from National Rail rather than TfL. If doing the former as for a manual check of the ticket at the barrier as the automatic ones will retain the ticket.