The UK Customs and Excise website contains information on allowances, travel safety tips, and contains downloadable documents and information.
There are no limits on the amount of duty and/or tax-paid alcohol and tobacco that you can take back to the UK as long as they are for your personal use or as gifts, and they are transported by you.
However, in the UK, Customs do attempt to limit the amount of alcohol and tobacco that is regarded as reasonable for personal use. This amounts to:
1kg of tobacco
110 litres of beer
90 litres of wine
10 litres of spirits
20 litres of fortified wine
More information is available in a pdf document downloadable at www.hmrc.gov.uk.
NOTE: This information is given in good faith, but no responsibility can be accepted in the event of changes effected by HMRC.
Visitors from North America will find useful information at http://www.travel-tips-packing-luggage.com/passport-information.html