The council has warned it faces “catastrophic financial consequences” if the work is not completed in time but has said it cannot put a precise figure on the penalty it would face under a £2.2bn PFI contract with Amey for highways improvements across the city.
But Councillor Bryan Lodge, cabinet member for environment and street scene at Sheffield City Council, told BBC Radio Sheffield: “It could be into millions.”
It comes after a High Court judge granted injunctions against three tree campaigners, as well as “persons unknown”, to prevent ‘direct action’ against felling in which protesters stand directly under threatened trees to stop work going ahead.
Such protests have stopped hundreds of trees across the city being removed in recent months but Mr Justice Males agreed with Sheffield Council’s argument that campaigners entering “safety zones” around trees to stop felling represented an act of trespass.
The council has warned that it must now complete work to remove and replace 6,000 street trees by the end of this year, with around 500 left to still be removed. If not, it says it will be in breach of its PFI contract with Amey, which is due to move into a 20-year “maintenance” phase from the start of the next year.
While the council insists only trees that are dead, dying, diseased or dangerous are being removed and then replaced, protesters have argued that many do not need to be chopped down and the work is being carried out as a cost-cutting exercise.
Councillor Lodge said it is not possible to put a precise figure on what the financial penalty would be should the delays mean the work overruns.
“The financial consequences of not completing the Streets Ahead Core Investment Period programme by the end of the year are potentially very significant but would depend on the extent of changes required to the programme in its entirety. An exact figure could only be determined once a review of the situation is carried out at the end of 2017,” he said.
“We are working tirelessly to avoid this situation as we know the majority of people in Sheffield support the Streets Ahead programme and want us to get the job done.”
He told the BBC that issues such as the council setting up an Independent Tree Panel to advise on removals and a court injunction which temporarily halted tree felling in early 2016 fell outside the delays in the contract that Amey, rather than the council, would be liable for.
Coun Lodge estimated that around £500,000 worth of council officers’ time had been spent on dealing with the tree issue.
It comes after the council said it had spent more than £150,000 on legal costs in relation to the most recent High Court case – money it is now seeking to recover from the three named campaigners; Calvin Payne, Green Party councillor Alison Teal and Sheffield Trees Action Groups founder Dave Dillner.
The council is also planning to seek damages from the trio following the civil case.
Mr Payne told the BBC that campaigners are still “weighing up their options” as they decide if they will appeal.
An announcement is expected later this week.
“In the last year, I have been arrested for the first time, I have been locked up for the first time, I have been in court for the first time, I have been cross-examined by a QC in the High Court. I have never done any of these things, this is entirely new to me,” he said.