Sustrans has started up an interesting-looking project called DIY Streets.
It seems to be based around converting existing streets following the Home Zone style, to make them friendlier with benches, more planting and slower traffic. Somehow they manage to achieve this relatively cheaply with a project in Bristol costing around £17,000.
More information on the Sustrans website here:
http://www.sustrans.org.uk/what-we-do/liveable-neighbourhoods/diy-streets
Also on the Guardian bike blog:
http://www.guardian.co.uk/environment/green-living-blog/2009/nov/25/diy-streets-clapton-sustrans
The nearest project is in Burngreave, Sheffield.