That site passes all of the usual checks. The domain name is long-established (since 2003) and the registrant's details aren't hidden. There's a postal address and phone number for contacts (rather than just an email address or form), and the email address uses the same domain name as the company (rather than a Hotmail or Gmail address). Credit cards and debit cards are accepted (rather than just PayPal or Western Union).
Further, the Consumers' Association website lists that retailer among other reputable names:
http://www.which.co.u...ncludingDelivery/asc/
(which I doubt they'd do if the trader was 'iffy').
For added security, pay by credit card and (as long as your purchase is over £100) you'll be able to claim against the card company if anything goes wrong.
Chris