Good evening to the one who prefers to remain nameless ;-)
Step 1:
Find out exactly who, in law, is the promoter. By that I mean you need to know whether it was a private individual or a limited company. Then get a postal address to go with that name. It should appear on the website but, if it's a limited company, you can also find the registered address here:
http://www.companieshouse.gov.uk/info
Step 2:
Send a formal letter (by registered post) to the promoter, demanding a refund. Your (dated) letter must clearly show your own name and address, together with that of the promoter. (If it's a limited company the letter should be addressed to 'The Company Secretary'). Your letter should also clearly state that if you do not receive your money within a designated period of time (I suggest 28 days) you will commence legal action. (Obviously you should keep a copy of the letter, together with the proof of posting).
Step 3:
If you don't get your money, commence legal action by using H M Courts Service's web-based system:
http://tinyurl.com/5kwx6
Chris