There are two types of IFAs. Some work on a commission basis (i.e. you don't pay them a penny; they get their money from the companies you invest with). Others charge customers a fee (but receive no commission).
Most people consult IFAs who receive commission but, of course, this does bring their 'independence' into question. (i.e. 'Are they really suggesting the best product or just the one which pays the most commission?'). Others prefer to pay fees, which may run into hundreds of pounds, in order to feel confident about the impartiality of the service.
The best way to find an IFA is, as EverClean says, to use the website of their industry body:
http://www.unbiased.co.uk/
Once you've entered your postcode, you'll be asked to specify the type of services you're looking for. You'll also be given the opportunity to specify whether you're seeking a commission-based, or fee-based, service.
Chris