I had my worktop fitted by http://www.whittonworktops.co.uk they too seem to be based in Yorkshire somewhere, but were far cheaper than the local London Firms. They said they come down to London most weeks.
I used http://www.whittonworktops.co.uk They were great value, and were quite a bit cheaper than the other quotes I got.... I found them by accident as they look to be based on the Westminster Bridge according to google maps.