Hi Gromit.
I didn't have a job when i got here, and I registered with every agency I could find. Adeco was horrible, and the rest were okay, but I don't know if they were all London based or not. I got my permanent job through Susan Hamilton, and my temp job through an agency called Action First.
At work, I hire temps through Huntress, which I think is absolutely fabulous.
I did have to lower my standards and get in on the 'ground level' but I managed to find a job at a place where I knew hard work would be rewarded. I also found work in a familiar field, which helped. Two years on, I've worked my way up and am now back where I was when I left the US.
Hope that helps!