Work to build a new multi-storey car park at Crown Street near the heart of Ipswich town centre is still scheduled to start early in the new year after the final size of the building is decided later this year.

The final size of the new car park will be decided at a meeting of the council’s executive in the early autumn. It will either have an extra floor, increasing the number of spaces from 236 to about 470, or an extra two floors which would push its capacity to about 700.

The council is still undertaking a feasibility study to find out whether enough businesses in the town centre would be prepared to take out season tickets for a larger car park.

Work on the project is expected to start in January, shortly after the end of the Christmas shopping season, and it should be completed in time for the Christmas shopping season in 2016.

During the work the current Crown surface car park – one of the busiest in Ipswich – will be closed but the site of the former police station, which is currently being demolished, is expected to be a temporary car park during the construction.

Ipswich council leader David Ellesmere said: “Everything remains on schedule for the new car park to be built next year. The report should be ready for us in the autumn and that will allow us to get things under way.”

The new car park is seen as vital for the town centre – not just as somewhere for shoppers to leave their vehicles but also for visitors to the museum and to the Crown Pools which are next door.

There is likely to be pressure for an improvement to the pedestrian entrance to Crown Street, which is currently seen as dark and threatening, especially on winter evenings.

The original Crown Car Park was built in 1974 and had about 600 spaces. It was the largest car park in the town.

Within a decade of it opening, it was discovered that there were serious structural problems – it was a victim of “concrete cancer” when the structure was decaying internally.

Repair work was carried out regularly, but in 2009 a survey revealed it had major structural problems that were beyond repair and it was closed immediately.

It was demolished a few months later and the site has been used as a surface car park since 2010 – but the council has always said it should be rebuilt.