The by-election being held in Ealing Southall today was caused by the death of the sitting Labour MP, Piara Khabra, the oldest politician in the House of Commons.

The timing of the contest makes it particularly crucial for all three main political parties, with all leaders having much to prove.

Having just taken over as Prime Minister, Gordon Brown has experienced an early bounce in opinion poll ratings and is anxious to attain a good result in a safe Labour seat which it held at the last election with an 11,440 majority.

In contrast, David Cameron is going through a rocky patch as Conservative leader having experienced a dip in the polls for the first time, and run into arguments with his party over grammar schools and proposed tax benefits for married couples.

The Liberal Democrat leader Sir Menzies Campbell, meanwhile, is said to be fighting for his job amid accusations that his party has been going backwards since Mr Cameron's election and claims that he lacks charisma.

With party leaders and Cabinet members going down to the constituency on several occasions each to canvas over the last few weeks - and with revelations of police investigations, and recent donations to Labour by the Conservative Party candidate - today's by-election has thrown up some eye-catching headlines. Some of the most eventful moments of the campaign include:

* July 4 - David Cameron appoints wildcard: The Tory leader stunned pundits by appointing Tony Lit, a 34-year-old Sikh businessman who had only been a member of the party for 10 days, as his candidate. Mr Lit was revealed to have come from a business dynasty worth £75million, according to the Sunday Times Rich List. His ethnic minority status, however, was thought by Tories to be an advantage in a seat with one of the highest proportion of Asian residents in Britain.

* July 11 - Labour politicians defect to Tories: Two local Labour politicians, Parmod Kad and Sarbjit Singh Gill, defected to the Conservatives, boosting Mr Cameron. However, The Times revealed that plans for a prominent unnamed Hindu to defect had been scrapped when he changed his mind.

* July 14 - Cameron candidate gave Blair £4,800 donation last month: In an extraordinary revelation, it emerged that Mr Lit attended a Labour fundraising bash in a business capacity as managing director of the Asian radio station Sunrise. The station wrote out a cheque to the Labour Party for £4,800 at the event, which saw Lit pose for photos with Tony Blair when he was Prime Minister. Mr Lit stressed that he was representing his company and had no sympathies for the Labour Government. Labour branded him a "Tory playboy".

* July 18 - 'Dirty tricks' allegations overshadow final campaigning day: The Conservatives accused Labour of orchestrating an staged ambush on David Cameron during a walkabout earlier this month, after identifying the woman who confronted him as a Labour supporter.

* July 19 - Police investigate electoral offences: Scotland Yard says that an allegation of “possible electoral offences” would be “thoroughly investigated”. The complaint related to claims by a Labour official that the Tories had broken electoral law by disclosing postal vote results. Under the Representation of the People Act, which governs elections, it is illegal to publish statements relating to the way people have voted before the close of polls.

A full list of the candidates standing in today's election are: Nigel Bakhai (Liberal Democrats), John Sydney Cartwright (Official Monster Raving Loony Party), Sati Chaggar (English Democrats - Putting England First!), Salvinder Singh Dhillon (Respect), Sarah Janet Edwards (Green Party), Kuldeep Singh Grewal (Independent), Tony Lit, (Conservatives), Yakub Masih, (Proclaiming Christ's Lordship), Jasdev Singh Rai (Independent), KT Rajan (UK Independence Party), Virendra Kumar Sharma (Labour), Gulbash Singh (Independent).

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