The future of the Upper Orwell Crossing in Ipswich should be decided in December after the cost of the project increased from nearly £97m to £139m.

The new figure was confirmed in a study commissioned by Suffolk County Council from engineering company Jacobs.

The government has pledged more than £77m for the project with the county making up the rest – but this effectively pushes the council’s proportion of the bill up from £19m to nearly £63m – a figure that was beyond its budget said council leader Matthew Hicks.

He said: “We are going to spend the next few months taking to the Department for Transport, the New Anglia Local Enterprise Partnership, (port owners ) ABP and other potential funders to see if they are prepared to put more money into this project.

“There will then be another paper brought to the December meeting of the county’s cabinet.”

Transport Secretary Chris Grayling said earlier this year that there was not going to be any further money coming from his department for the project.

However Mr Hicks said the costs of the project had increased because of the complexity of the proposals and delays to the survey work.

“We are now at the position where we cannot make up this funding gap on our own.”

But he promised that a decision would be made in December so home and business owners on either side of the proposed crossing would know then what was going to happen.

Business organisations in Ipswich and Suffolk have been lobbying for the project to go ahead – but residents living on either side of the river have been campaigning to get the project dropped.

Ipswich Central chief executive Paul Clement said: “A majority of town centre businesses support the Orwell Crossings project, seeing it as aspirational and traffic-reducing. Given the current risk to the scheme, it is imperative that the County Council’s financial commitment to Ipswich is not lost.”

Former Conservative leader on Ipswich Council Liz Harsant has joined residents in her Holywells ward to oppose the new crossings. She said: “I am pleased for the residents because I cannot see this kind of money being found by December – it will be a weight off their minds.”

Ipswich Labour MP Sandy Martin said Mr Hicks’ proposal seemed very sensible: “There is clearly support from some of his party colleagues for these crossings so he has to be seen to be doing all he can – but I don’t think it is very likely that he’ll be able to come up with another £43m.

“And to be honest, if there is that kind of money around for Ipswich it would be better to spend it on a project that would really benefit the town, like the northern by-pass.”