A controversial review launched by the new Scottish Parliament has cast doubt on whether the Edinburgh Airport Rail Link (EARL) project will go ahead, particularly with value-for-money concerns weighing heaviest on the selected, and most expensive, option to build in tunnel.

The threat comes despite the EARL project having received Royal Assent to proceed, in April, paving the way for construction to start next year for completion in 2011. Project development work is being continued with funding still coming from the government-funded agency Transport Scotland.

EARL would be a strategic transport project linking 62 rail stations directly to the airport, including from the west coast. The tunnel element would be a 1.6km link of 6m i.d. passing under the runway with a cover of about 8m. For the link, two 715m long tubes were to be driven through mixed boulder clay, with cut and cover sections at the ends.

The reference design was being finalised when the election took place. General Arrangement drawings were to have been completed by around August for a call for expressions of interest to be issued at the beginning of 2008.

However, the unprecedented success of the Scottish National Party (SNP) in achieving victory in the national elections, held in early May, has changed the strategic landscape for public transport projects. This has come despite the previous parliament having signed off on the project and SNP leading a minority government. Bipartisan debates have erupted in the new parliament as a result of the project review.

The political party had expressed opposition to the tunnel option for EARL due to costs and almost immediately upon the new parliament sitting it launched a review of the project, citing concerns over value-for-money for taxpayers. It requested an audit review, which was expected to report on 20 June. The agency charged with developing EARL – tie – said that the tunnel option, although the most expensive offered direct links for travellers and showed the greatest benefit to cost ratio, being 2.16 to one.