Under the leadership of Bill Bryson, the Campaign for the Protection of Rural England is probably the leading organisation campaigning against litter and fly-tipping. Their "Stop the drop" campaign is the highest profile activity on this front for many years.
Litteraction supports and promotes local litter picking groups. There's an interactive map to find you nearest litter picking group, the facility for local groups to set up web pages and a forum for exchanging ideas.
Britain's not tidy and it sounds like something your Mum would say about your bedroom, but this is still a very useful site. There is a lot of information on legislation and they have done some useful research into littering. Unfortunately, their guide to litter picking is guaranteed to put you off...first get your liability insurance, then do your risk assessment, then get your antiseptic wipes, then arrrange your first aiders...
I think BBC Radio Suffolk's "Don't be a Tosser" campaign sets the gold standard for anti-litter campaigns. It's imaginative, engaging, fun , not at all nannying and had done a great job of mobilising a wide range of community groups. Outstanding! Well done guys.
The Litter Project is the brainchild of Elizabeth Mullen. She's american, but it is a great idea all the same - inspire 100,000 people to pick up one piece of litter every day (that'll be 36.5 million pieces every year).
Rob Kevan clears litter from his home town of Llanwrtyd Wells and has done some high profile litter picks on Snowdon, Ben Nevis and the walk in to Everest in Nepal. He's a great guy and the nearest thing to an A list litter picking celebrity.