Extra funding could be needed for a scheme to prevent traffic crawling through the middle of an ancient monument and a major revamp of the area around it.
Plans to redevelop the Southgates area of King's Lynn could see the main London Road diverted to avoid the South Gate and a busy roundabout replaced by new junctions.
The government has agreed £24m in levelling up funding for the scheme, which also includes pedestrianising the area around the 600-year-old monument.
But a 170-page report to West Norfolk councillors warns of rising costs and recommends allowing officers to investigate further sources of funding to progress the proposals.
It comes after almost 80pc of the hundreds taking part in a public consultation agreed with re-routing the road to allow the historic gate to become a tourism destination.
The full Southgates Area Masterplan also includes different options for the roads around the site - including replacing the Southgates roundabout with junctions.
The report says: "The final development brief has drawn together the vision and design principles to set out a schematic development layout to transform the site and enhance the setting of this historic gateway to King’s Lynn."
But the report says further public funding will be required. While no figures are given, it says grants may be available from other financial pots including the government's Shared Prosperity and Brownfield Land Release Funds, Homes England and the Community Infrastructure Levy.
It adds: "The next steps will involve testing and completing more detailed appraisals as greater scheme information is developed, including evaluation of abnormal costs, a full cost schedule; and so also to reflect changes in construction costs - which are subject to significant inflation at present - and the property market."
Councillors on the regeneration and development panel are being recommended to agree for officers to investigate further sources of funding when they meet on Tuesday, April 11.
The final proposals are expected to come before the council in early 2024.
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