For, at the current rate of house building, it will take the council 117 years to raise the £8.75 million it must contribute by 2038.

In 2004, the council agreed in its business case for the line’s reinstatement to commit £7.4 million to the project’s construction.

That cash was to be raised from “developer contributions” levied against successful planning applications for new houses which would benefit from the railway.

That funding commitment has risen to £8.7 million, capped at 2012 prices, with the cash due to be phased in annual payments to Transport Scotland which is fully funding the £353 million railway. The first payment of £1 million is due in September, 2016 – a year after the trains start running.

But the Border Telegraph has learned that, in the past 10 years, the total developer contributions raised have totalled just £743,127. And if the past decade’s level of housebuilding is maintained, the grand total of developer contributions collected by 2038 will be £2.56million – leaving SBC £6.19 million short of its commitment.

Based on the current levy of £1,734 per unit – with new affordable housing exempt - a staggering 4,617 contributions would be required over the next 24 years for the council to meet its target.

Imposed originally in the Central Borders Housing Market Area (HMA), the developer contributions were extended to the North Ettrick and Lauderdale HMA in 2006 when the railway legislation confirmed the inclusion of a station at Stow..

The project’s business case states clearly that the councils in Scottish Borders and Midlothian (whose contribution has been set at £22.25million) “will be responsible for any deficit after all development contributions are handed over the Executive [now Scottish Government]”.

This week, opposition councillors expressed concern at the possibility of SBC facing a £6 million shortfall.

Conservative group leader Michelle Ballantyne (Selkirkshire) told us: “I don’t know if the railway will be the huge economic boost that the SNP believes it will be and I certainly have my doubts.

“I do know, however, that we will pay a heavy price with more cuts to our services if the business plan for the railway is as flawed as it appears to be.” And fellow Tory Gavin Logan (Tweeddale East) said: “This is so serious that the council’s SNP-led administration will have to make a contingency plan as a matter of urgency.

“We need to know what happens if the council defaults on its pledge to contribute £8.75 million and we must ensure we don’t saddle future councils with a millstone round their necks.” Mr Logan said he would be demanding clarification of the position – and details of any Plan B – at next month’s council meeting. But Councillor Stuart Bell (SNP, Tweeddale East), SBC’s executive member for economic development, hit back, claiming: “It’s a bit early to get alarmed about underpayment.” He told the Border Telegraph: “The Borders Railway will boost economic activity in the central Borders and, as a consequence, it’s anticipated that there will be an increase in house-building to accommodate a population increase.  “The housing market throughout the country is cyclical with peaks and troughs and the market in the Borders is no exception. It will come as no surprise to anyone that as we have just been going through the worst economic recession in a generation - in part exacerbated by the policies of the Westminster Tory government -  there has been a slow-down in housing completions.

“Inevitably, that slow down will be followed by growth as the economy recovers and we need to see the real economic impact of the railway once it is operational.

“It should be remembered that the £8m we have still to find for the railway should be put in the context of the £10 billion which the council will spend over the next 30 years.

“We will be able to budget for any shortfall in railway contributions, should they arise and, if necessary, negotiate adjustment to the payments in line with variations in house completions and developer contributions.”