The controversial £610m project to provide direct rail links to Edinburgh Airport from all over Scotland was given the green light yesterday.

However, SNP politicians pledged to stop the project in its tracks if they win power in the Scottish elections in May.

Transport Minister Tavish Scott spoke in support of the Edinburgh Airport Rail Link project (Earl) and although he conceded the final cost may rise to £650m, pledged it would not spiral out of control as the construction of the Scottish Parliament had done.

However, SNP politicians said it was a waste of money and the cash would be better spent improving public transport and repairing the roads.

Mr Scott denied this and claimed the time was right to push ahead with the plan, rather than prevaricate, which was what he accused opposition politicians of doing. His comments came during the final stage debate on the Edinburgh airport rail link at the Scottish parliament, after which the plan was approved by 86 to 29 with three abstentions.

Royal Assent for the bill is likely to follow in the coming weeks. Preparatory work is expected to start later this year, with trains serving the airport by the end of 2011.

Mr Scott said: "The airport will be linked directly to 14 local authority areas with a total population of 3.2million people and 64% of the total Scottish population.

"The rail link will remove 1.7million car trips from the roads, helping to tackle the environmental and economic impacts of congestion.

"Businesses which compete in the global market such as tourism, financial services, bio and life sciences will find access easier both into and out of Scotland."

Mr Scott said that because Edinburgh Airport was predicted to grow from eight million passengers in 2004 to potentially 23 million by 2030 there was a need for a genuine public transport alternative to the car.

However, SNP transport spokesman Fergus Ewing said the project did not represent best value for taxpayers' money. He said the estimated cost of £610m was made in 2005 and that "very few" commentators now believed that it could be delivered for less than £1bn, despite Mr Scott's assurances on finance.

"The money can be better spent on other projects," said Mr Ewing. "We urgently require to improve our rail and road systems in Scotland."

Tory transport committee member David McLetchie said he was sceptical about the need for both a rail link to Edinburgh airport and a tram line, considering a good bus service was already in place.

Meanwhile, the Glasgow Airport rail link has already been given Royal Assent. Construction will start next year.