Based on the Wikipedia page .
The Act was brought in after a referendum, held under the Greater London Authority (Referendum) Act 1998, had resulted in a 'yes' vote. Apart from the main provisions creating the authority and transferring powers to it, it also created a Metropolitan Police Authority for the Metropolitan Police Service, and consequently altered the borders of the Metropolitan Police District to be coterminous with Greater London (excluding the City).
It was the longest Act to be passed by Parliament since 1935.
- Official text of the Greater London Authority Act 1999 as in force today (including any amendments) within the United Kingdom, from the UK Statute Law Database. (Note: may not be up to date.)