The Greater London Authority (GLA) is comprised of two parts: the London Assembly and the Mayor.
The GLA's home on the south bank of the River Thames
The Mayor and his team have an extraordinarily diverse brief, which includes oversight of many aspects of London's transport network, from investment in tube services to the level at which black cab fares are set.
They are also responsible for the preparation of plans to cope with disasters in London, boosting wealth creation in the city, promoting London's image as a cultural hub, supervising the work of the police and deciding whether new skyscrapers will be built.
Members of the London Assembly, meanwhile, have the important role of scrutinising the Mayor's decisions. There are 25 of them: 14 represent constituencies; 11 are elected from party lists.
One way they carry out this scrutiny is to challenge the Mayor at
regular two-and-a-half hour question sessions
in City Hall. There are 10 of these sessions each year.
They can also carry out detailed investigations on matters they feel merit attention and have the power to demand that documents about the workings of the Mayor's team be made available to them.
But the GLA does not have the power to change the law: the roles and responsibilities of the Mayor and the London Assembly are defined by legislation passed by the UK Parliament in Westminster.
Question time: the Mayor faces a horseshoe-shaped table of inquisitors
This legislation also ensures that the UK government can step in and take over if ministers feel that the Mayor is not fulfilling the role properly.
The funds needed to run the GLA and realise the Mayor's spending plans are provided partly by a levy on council tax in London boroughs and partly by government grants.
The Mayor needs the London Assembly's approval for his budget each year. The Assembly has the power to amend the Mayor's budget, but there must be a two-thirds majority for this to happen, which makes such an amendment very unlikely.
Unlike the UK Parliament, the GLA has fixed terms. Every four years, Londoners go to the polls to give their verdict on the Mayor and the Assembly. The next election is due in May 2012.
The Mayor's salary for the current financial year is £143,911. Assembly Members are paid £52,910.
The GLA works closely with local government on certain issues:
• All planning decisions are taken locally, as they are elsewhere in the UK. But, for big building projects in London, the Mayor must be consulted and can over-rule local authorities, who are supposed to ensure that they comply with his "spatial development strategy".
• The provision of fire services and strategies for dealing with emergencies in the capital are the responsibility of the London Fire and Emergency Planning Authority (LFEPA), which is directly accountable to the Mayor. The 17 members of the Authority are appointed by the Mayor; eight are nominated from the London Assembly, seven from the London boroughs, and two are Mayoral appointees.
• In collecting and disposing of waste, local authorities must take into account the Mayor's policies on waste management.
Influencing the GLA
There are several ways to lobby your representatives on the London Assembly.
You can provide evidence for their inquiries, suggest questions for Assembly members to ask the Mayor, present them with a petition, or even challenge the Mayor yourself at "People's Question Time".
More information is available on the