Whenever I'm in London, I try to drop by this beautiful grocery store on 42 Amwell Street, near Angel. Catherine Conway set up 'Unpackaged' in 2006 so that customers could refill their groceries using their own containers.
You can take in any old container to shop with (as long as you've rinsed it out first)... Then you simply weigh it at the counter before you start shopping and the weight is taken off at the end. Easy!
For those of you in London - look out for Unpackaged at street parties in the Islington area throughout the year or keep your eye on their facebook page for details...