The SNP has selected its longest-serving Glasgow councillor to try to overturn a 13,507 Labour majority in the by-election for the Westminster seat of Glasgow East in three weeks' time.

John Mason, who beat off two other contenders for the nomination, leads the Nationalist group on the council. If he succeeds on July 24 it will spark a massive crisis for Labour and could even topple the Prime Minister, Gordon Brown.

Councillor Mason, 51, from Rutherglen in the south of the city, is an accountant who has lived in the East End of Glasgow for 18 years. He has been a councillor since winning the Garrowhill ward, also at a by-election, in 1998.

The constituency Labour Party meets tonight to select its candidate. The favourite is George Ryan, 45, a councillor in the Shettleston area of the constituency.

The Liberal Democrats have selected Ian Robertson, a 30-year-old maths teacher. In the 2005 general election they came third, 1,603 votes behind the SNP.

The Scottish Tories have selected Davena Rankin, a research and commercial development manager at Glagow Caledonian University.

The size of the Labour majority makes the seat the 25th safest of all 646 constituencies in Britain but, after recent heavy defeats in the Crewe and Nantwich and Henley by-elections, and the resignation of Wendy Alexander, Labour's Scottish leader, many in the party are nervous.

Labour will be desperate to keep the campaign focused on local issues such as improvements in housing, the fight against street crime and combating the drugs epidemic in the area. The Nationalists will want to put Labour on the back foot on issues such as the rising cost of food and fuel, the credit crunch and continuing social problems in the area despite decades of local Labour rule.

The campaign proper will get under way next week when all parties have candidates in place, but Labour moved quickly yesterday with an attack on the SNP over job losses in the Glasgow Science Centre, which is to cut 28 posts as a direct result, it says, of a 40 per cent reduction in funding from the SNP government.

Kirk Ramsay, the centre's chief executive, said: “This announcement marks a very sad day for Glasgow.”

The centre received £1.7 million in 2007-08, but this will be reduced over the next three years and would fall to £1.08 million by 2010-11.

About 480,000 people visit Glasgow Science Centre every year, with 65,000 schoolchildren taking lessons there. Another 60,000 in disadvantaged areas of the East End benefit from its outreach programme.

A Scottish government spokeswoman said that it was planning to bring in what she called a fairer and more sustainable funding package for science centres in Scotland, with £7.6 million over three years to be shared between the four centres - Glasgow, Edinburgh, Aberdeen and Dundee. Glasgow Science Centre would receive approximately half of the cash.

Mohammad Sarwar, the Labour MP for Glasgow Central, accused the SNP of making outrageous cuts.

“The Labour Government is doubling its investment in science, whereas the SNP is letting Glasgow and letting science down. Their decisions are beyond belief”, he said.

Ladbrokes make Labour and the SNP joint favourites to win the seat, with both at 5-6 on. It originally made the SNP clear favourites with Labour as the 6-5 outsiders.

David Williams, of Ladbrokes, said: “Punters haven't yet abandoned Labour in every political market. All the early Glasgow East money has been for a rare Gordon Brown triumph.”

The SNP, meanwhile, claimed that the Prime Minister was “wobbling” over fuel duty after telling a Commons committee yesterday that he would look closely at the issue over the next few weeks. “The rise in fuel duty must be scrapped,” said Angus Robertson, the SNP MP for Moray.

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