I assume you are asking about how to convert your BTC into GBP.
For small quantity, you can do a direct sales at one of the many bitcoin community forum, such as bitcointalk.org (particularly, the Currency Exchange sub-forum). There is currently an active thread on the forum, where someone is buying large quantity of bitcoin and payment via cash deposit into your UK bank account.
For large quantity, you should check out major exchanges, such as MTGOX, and receive your money via Bank Wire.
Accepting payment via Paypal and other reversible transfer services should be avoided, as the buyer can take your bitcoin and reversed the payment at a later date.
1Sellers are only accepted if they are dedicated and not just once-offs. – whiskers75 – 2013-12-09T15:47:30.520