As Eddie indicates,there are plenty of websites which supply beer by post but you're likely to encounter a problem over payment. Most companies won't send purchases, made via a debit or credit card, to any address other than the one to which the card is registered. You might however find a company which will send beers direct to the intended recipient if you post them a cheque or postal order.
Interflora works by having a network of local, independent traders who all offer deliveries. I can't think of any similar traders who deliver beer. However, if you'd consider sending wines or spirits instead, Interflora can still help:
http://www.interflora..._id=2124587;showall=1
As long as there's no great rush (because you'd still have to get your order despatched to yourself and then post it on) my own preference would be to send J D Wetherspoon gift vouchers. That enables the recipient to choose his own beers (either to drink in the pub or to take home) or, if he prefers, to have a meal instead:
http://www.jdwetherspoon.co.uk/home/vouchers
Chris