The former building society was formed by the merger of the Alliance Building Society (originally based in and called the Brighton & Sussex) and the Leicester Building Society on 1 October 1985. In 1990, the society acquired Girobank, a major provider of cash-handling services to the government and large companies and current accounts, from the Post Office. With other large building societies such as Halifax and Woolwich, Alliance & Leicester decided to float on the London Stock Exchange, generatingwindfall payments to members worth up to £5,000 each. Flotation took place on 21 April 1997.
Info gleaned from Wikipedia