A secret network of cellars and uncharted pipes are to blame not only for delays to the Temple Quarter Enterprise Zone development, but also increased costs.

The major regeneration of the long-neglected area around Bristol Temple Meads is expected to bring jobs and opportunities to the city, but for commuters it has meant ongoing disruption.

Now cabinet papers have revealed the cost of completing the full infrastructure programme for the redevelopment is expected to reach £28,145,289 – almost £3 million more than allocated – due to “unforeseen works”.

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Bristol City Council says various mitigating actions have been identified to reduce the potential overspend and cabinet members agreed on Tuesday to use £1.45m of the transport budget for next year to help plug the remaining shortfall.

Addressing the meeting at City Hall, deputy mayor Craig Cheney said: “There have been many problems discovered in delivering this work, particularly finding things like basements under the roundabout at Temple Gate that needed to be secured and have inevitably delayed it. Also unexpected, uncharted and unmapped gas lines and services underneath the ground.

“In terms of addressing the budget shortfall, the recommendation is that we use some of the transport team’s funding for next year to address £1.45million of the current shortfall.”

He added: “Most Bristolians will probably be thinking ‘let’s get that roundabout and section finished now’.”

At January’s cabinet meeting, it was revealed that demolition of the former sorting office to make was for a new university campus in the Temple Quarter Enterprise Zone is expected to incur additional costs, the details of which are still unknown.

Welcoming progress on work in the area, mayor Marvin Rees said: “It’s going to take 18 months but by this time, there will be a different sight across Bristol – one which shows that things are getting done.”

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