Duplicate thread here - this one and "UK Anti Bush Protests" - so I'll post my reply to akenaton here.

Interesting to hear Will Self on BBCTV,harangue anti Bush protesters. He reckons they are wasting their time,and should be trying to de-select Blairite parliamentary candidates.I think I agree with him ...

The purpose of demonstrating is primarily to show Americans that, whatever they may have been told, there is very little popular support for Bush in this country.

Mind you might even help Bush among those Americans who don't much like the UK. However the impression I have got is that it's seen as quite important to assert that America does have some significant backing abroad, which is very questionable; and even that Bush is held in high esteem, which is certainly not true.