A £45 million project to end the "West's rail bottleneck" and boost the economy of Gloucestershire will take four months longer than first planned after engineers were called away to deal with repair works elsewhere.
The project to "re-double" an 11-mile section of railway will not now be finished until August, rather than the planned completion date of this Easter.
The work between Swindon and Kemble was delayed by a host of problems, including bad weather and a de-railed engineering train. And because the teams from the Kemble project have been assigned new engineering works jobs for Easter, they will take a break and return later to finish the job during the summer.
The line through north Wiltshire connects Stroud, Stonehouse, Gloucester and Cheltenham with the Great Western mainline at Swindon, but the service to the capital from Gloucestershire has been limited – something that politicians and business leaders said was holding the county back economically.
The line was made a single-track line in the 1960s and after years of lobbying for the work to take place, money was eventually found – primarily from the controversial ditching of the £35 million road bypass of Westbury, further south in Wiltshire.
The doubling of the line will mean electrification work can also take place, but politicians said the news of the delay was "frustrating".
A spokesman for Network Rail, which is dealing with a similar four-month delay on a single project to replace a bridge on the mainline on the Wiltshire-South Gloucestershire border at Acton Turville, said a high volume of engineering and problems with the wet winter caused the delay.
"We are now working towards completing the scheme between Swindon and Kemble by August, rather than Easter," he added.
Cotswold MP Geoffrey Clifton-Brown said he had been monitoring the work just over the border. "Obviously I am very disappointed with this news. I will be pressing Network Rail to make sure that the completion date does not slip any further," he said.