I think you'd have a hard time making the streets near me more dirty! I live too close to pubs and clubs... not a nice place to be on a saturday morning.
Of course, if you are going to visit the UK, you have to promise not to judge us all by London, and learn about the north/south divide! (and that the North is great!)

I've been to London and a number of small towns in the UK visiting relatives. This was a decade ago, but I remember it looking rather clean.
If you come to Aus and my state, be sure to go to the Adelaide CBD and eat at McDonalds. @ 3am :)