Not to worry, this isn't the soap opera itself, so you won't be lost trying to figure out what's going on. It's something else entirely.
There's a very big, annual charity telethon broadcast on the BBC in the U.K. called Children in Need. And as far as I can tell, from what little detective work I could manage, every year the cast of EastEnders puts together a hugely elaborate musical production number, whether or not all the actors are especially-accomplished with singing, let alone dancing. But that seems to be some of the fun, watching actors a bit out of their element throwing themselves into such a big production all for a good cause -- and mostly it's quite well done. And did I say elaborate? They really put a major effort into this. I've watched several of the videos from different years (and will post a few others), and they're a joy.
This is one of my favorites. It's a a tribute to the West End theatre district, and I'll leave it to your discovery what shows are included. I believe this came from the 2008 broadcast.