I live in NYC and go to shows every weekend pretty much - so I have seen the big high dollar productions all the way to the other side of the spectrum of little black box productions.
I'm looking for recommendations on seeing something in London that 'only you can see there and it's truly British' and it wouldn't ever come to NYC. For instance - I'm not going to go see 'Aladdin' in London as it's on stage here in NYC.
Where do I go to look for the true British/English/UK plays/musicals etc?
My lovely spouse got a single ticket to Dreamgirls on her most recent visit to London in March without much trouble. it was a night when Amber Riley was not performing (website says this is normally Monday - but that is not a guarantee). The primary alternate, Marisha Wallace is reportedly sensational. There is a West End twitter account that announces standbys and understudies for most shows. It is "West End Understudies
Also, I think there is a plan to transfer the show to NYC, so Dreamgirls does not fit this thread..
The TKTS booth - is it crowded like NYC Times Sq - would I need to stand in line for several hours if I chose to stop by and see what they had on the board?
We just retuned from London and saw four shows, many of which you could or could have previously seen in NY. The real standout that is London-specific, however, is Twelfth Night at the National Theatre. It was an absolute delight and I highly recommmend. Locals in the crowd compared to the other shows we saw and just a terrific production. If it is still around when you go, I'd catch it!
You could also try something at Shakespeare's Globe as the season will be starting in late April.
We walked by TKTS once and it wasn't crowded, though we didn't use it. We did use the Today Tix app and it was a great experience. Unlike when you use that app for NY, it shows you the precise seats you're buying on a map. Aisle seats for the win!
We never used the TKTS booth. You can check it online to see if there are any discounts there. People report good deals with TodayTix - but I never used it. Timeout London sometimes has some pretty good deals. We primarily used one of the LondonTheatreBooking booths - in particular the one at Picadilly Square in front of Boots, although the one on Charing Cross was also good. They did pretty well at discounts and showing you tickets and even negotiating with the box office. But, we got discounts by either doing day seats (check Theatremonkey.com for info) or simply asking at the box office. You can ask "any day seats left" and depending on the show, they may give you a day seat or a day seat price for other seats. The box office staffs, in general, in the West End were really nice and cooperative - so long as you are nice and not demanding.