To know your options, the following factors are relevant:

 - Where are you located (country)?  [Edit: Site title, shows UK]
 - How much are you looking to buy?
 - What payment methods do you have available or prefer (e.g., cash, bank transfer, etc.)
 - How soon do you need your bitcoins?
 - Is privacy important?



BlockChain.info now accepts funds using a bank transfer (Faster Payments) or from Barclays Pingit:
 - https://blockchain.info/wallet/deposit-bank-transfer
 - https://blockchain.info/wallet/deposit-pingit

Also, you can send cash (GBP) in the mail to Bitcoin Nordic (in Denmark):
 - http://www.BitcoinNordic.com

There is BitBargain market:
 - https://bitbargain.co.uk/buy

And BitcoinFridge:
 - https://bitbargain.co.uk/buy

And, or course, there may be a chance for a local trade:
 - http://www.LocalBitcoins.com

Including individuals who trade GBP frequently:
 - Tenakha  https://bitcointalk.org/index.php?action=profile;u=65105

There are a number of options:
 - http://en.bitcoin.it/wiki/Buying_bitcoins