Hi, thanks for your question. My name's XXXXX XXXXX I'm going to assist you with it.
Unfortunately, there is no way to be 100% certain of legitimacy but checking that the relevant UK company exists is a good start. The UK company referred to on their website does, indeed exist. It was registered in May 2012. As at February 2013, it was dormant (which means that, at that date, it was not trading). There is no information regarding trading since that date because accounts are only submitted annually.
Of course, the relative youth of the company and the lack of trading may mean nothing. If they are an international venture, they may only recently have found the need for a UK subsidiary. Or it could be that they don't need a UK subsidiary at the moment and are just protecting the company name for when they do. It's impossible to tell, so the botXXXXX XXXXXne is that you should not read too much into this.
Other things you can do to check the legitimacy of a company are:
Search the company name and its services on a search engine such as Google. See if it shows up on any sites that have reported the business in a negative context. You may also come across some helpful reviews on blogs or consumer sites (although you should still treat these with caution).
Conduct a thorough review of the company's website. Look for a professional approach and good English. You may also be able to find some testimonials about the services and products. Also look for an "about us" section to see how long they have been trading and who's behind the business.
Look at any written terms and conditions carefully. Depending on the nature of the service, they may well offer a money back period or guarantee. If they have faith in their services this may help you to garner some also. Also check out customer services (if they have one) by ringing the contact number. Ask as many questions as you need to get peace of mind.
Finally, trust your instinct.
As I say, there's no fullproof way of determining legitimacy and no "legal" answer to this but hopefully this information should help.
I hope this answers your questions. If so, please don't forget to rate my answer so that I can obtain credit for my work. Our conversation, won't end and you can ask me any further questions you need to clarify the above.