FACTBOX - Crewe and Nantwich by-election

LONDON (Reuters) - A by-election will be held in the Cheshire constituency of Crewe and Nantwich on May 22 following the death of Labour MP Gwyneth Dunwoody who held the seat for 34 years. Here are some key facts about the election.

Labour are defending a majority of 7,078 and the Conservatives need an 8 percent swing to win the seat. The seat is the 165th most winnable on the party's target list.

The Conservatives have made the government's unpopular abolition of the 10p starting rate of tax the focus of their campaign. But the sting may have been taken out of this issue following Chancellor Alistair Darling's 2.7 billion pound fix for the majority of the poorer households made worse off by the measure.

Losing the seat would make little difference to Brown's 67-member majority in parliament, but would be a huge psychological blow and could prompt a challenge to his leadership. The Conservatives have not gained a seat in a by-election since 1982.

The constituency of 67,000 voters is split between the former industrial centre of Crewe, famous for its railway station and locomotive building, and the more affluent market town of Nantwich.

Gwyneth Dunwoody's 49-year-old daughter Tamsin is fighting the seat for Labour. Her mother's reputation as a no-nonsense "old Labour" battleaxe is perhaps her strongest card -- Labour says she is a "chip off the old block". The Conservatives have portrayed her as an outsider -- she lives in South Wales but says she will move to Crewe if she wins.

Edward Timpson, 34, a father of three children under five, is the Conservative candidate. The local Labour party have chosen to highlight his wealthy background and call him a "toff". Timpson's family run a chain of shoe, key and lock repair shops in the Northwest.

Elizabeth Shenton, 43, a councillor and former bank clerk, is standing for Nick Clegg's Liberal Democrats. She has spent all her life in the area and shares her home with 10 cats.

(Reporting by Tim Castle; Editing by Steve Addison)