Some of the tests I use for checking out a website are listed in my post here:
http://www.theanswerb...7.html#answer-5432405
For web addresses with 'uk' in them, this is where to find some of the information:
http://www.nic.uk/other/whois/
For others, try this:
http://who.is/
Watch out for poor grammar or spelling (or for links which go nowhere) on a web site. Also take a look at the 'terms and conditions' page; rogue websites often simply copy and paste such pages from legitimate sites. If your see US spellings (and references to American laws) on a website which purports to be British, you should be suspicious.
However simply doing a Google search, with the word 'review' in front of the name of the website can often tell you a lot. Finally, posting a specific question here will get lots of people to check the site for you (or possibly to recommend it, if it's one that they regularly use without problems).
Chris