What to do Sunday evenings?

I would just go to a pub. No tour, no walking thing... not that those probably aren't cool - but the absolutely neat thing about pubs is that you can meet actual people and talk to them! Example - in January of this year, we settled in at a pub by Trafalgar Square (but not on a heavily touristed street) and wound up talking to a charming couple (both London natives) who gave us super advice about what to see and do - and what to avoid - around Charing Cross, advice about the best bus to take from the Stables Market, and tips on a great chippie a few blocks away. More importantly, we also had a really meaty discussion about politics, which was kind of awesome, since we got the non-US perspective on a bunch of interesting stuff. Then, to cap it off, the husband, who was facing the window, yelped, "Goodness me it's a Chelsea Pensioner!!!!!!" So my husband got to see a real live Chelsea Pensioner. Which is kind of a huge deal. Anyway, that wouldn't have happened if we hadn't gone down the pub, on our own, and been open to a conversational gambit. Oh - and if you choose the right pub, you can also get a good meal.

We were in London last April for several days including a Sunday. We took a train to Hastings (Charing Cross station) and spent the day exploring the area. You might consider that option or taking a daytrip by train to another outlying area. You could even go to York - that's two hours away by train.

London Walks offers 3 different tours on Sunday evenings: Soho Pub Walk at 7:00, Haunted London at 7:30 and Jack the Ripper at 7:30. £9 per adult. www.walks.com

Good ideas! I did a Sunday night London Walks pub walk, and it was a fine thing. Ours was in Chelsea, but I'm sure the others are also worth it. (Just a note, if you're drinking fruit juice or other nonalcoholic stuff: specify "no ice" or you may get a glass so stuffed with cubes that there's precious few ounces of liquid to drink.)

A different idea. Most churches in London have an evensong service early Sunday evening. They are fairly short, 30-40 minutes, and normally are almost all singing by a choir with only a brief sermon. The one at St. Paul's Cathedral is especially good and sometimes has the boy's choir. There is no charge, although an offering basket may be passed for donations.
At St. Pauls this also gives you a free glimpse at the beautiful architecture.

St. Bartholomew the Great in West Smithfield has an evensong service at 6:30 on Sundays. Its historic atmosphere adds another dimension to the music.