This symbol is not only used to designate the Sterling Pound, but also the Irish Pound. In the case of Irish Pounds, the L symbol is often prefixed with the letters 'IR' to avoid confusion with Sterling. For example:
The Irish Pound is also called the Punt, which is the name of the currency in the Irish language. The three-letter code for Irish Pounds is IEP. It's probably not worth memorising this fact, however, as the currency will cease to exist in 2002, when it is replaced by the euro.
The pound symbol itself may be rendered in HTML with either £ or latterly £