Cost of works on York ring road go up by £455,000

And it adds that work on the next six roundabouts could be “reduced in scale and scope” to keep the project within budget.

Improvement work was completed at Wetherby Roundabout - the first of seven roundabouts to be upgraded as part of the scheme - in February.

But the programme was hit by more setbacks than expected, including the need to remove tree roots, an area of the excavation flooding and an unexpected archaeological discovery, according to a report prepared for West Yorkshire Combined Authority.

Last July archaeologists said they believed they had found evidence of a prehistoric settlement at the construction site.

Part of the find is believed to date back to the Iron Age.

Researchers discovered decorated pottery fragments, a piece of possible pumice-stone and a volcanic rock not found locally at the site.

The report said it is an “unexpected regionally significant find”.

It adds: “In isolation the project contingency would have covered a single occurrence.

“The impact of multiple risks occurring at a greater level than anticipated when the risk allocation was identified ... has resulted in considerable unforeseen sums required to manage, mitigate, and overcome the various impacts of these risks.”

It goes on to say: “Subsequent phases of the programme have the potential to be reduced in scale and scope to remain within the overall programme budget.”

Extra costs included £187,496 more on earthworks issues and £79,085 on archaeology issues.

The full ring road upgrade scheme is set to cost £38m and is funded by the West Yorkshire Plus Transport Fund.

It aims to reduce delays and congestion as well as boosting York’s economy and taking traffic out of the city centre, according to City of York Council.

Monks Cross junction is due to be the second roundabout to be upgraded, but the council says it is only when all seven are completed that the benefits of the scheme will be realised.