Yes I have, and successfully sued them in the small claims court after I cancelled my order and they then sent it out and billed me six weeks after that and 'dragged their heels' on the refund. Got my money back and compensation.
I should in fairness point out that other than the product being dispatched very late,(I cancelled after waiting 2 weeks for dispatch for a lens they said was in stock) it was otherwise as ordered and would have been great.
I used the on-line service to sue them in in the small claims court, as I recall it was in Nottingham. I certainly had a UK contact address, (I believe they gave that to me in an e-mail exchange), for them to have the papers served. There was no actual court attendance. It was all mail.
The court agreed to my claim and gave them 60 days to respond, to contest, with a defence. They did not respond so the claim was deemed undefended so I 'won'. 2 weeks after that Simply Electronics paid me my refund, including postage and £50.00 in compensation that I claimed for my time and inconvenience.