More than £35,000 has been spent on repairs and investigations into why the A14 at Rougham has suffered subsidence.

The Highways Agency has revealed that cavities have been discovered under the road in an area where a drainage crossing trench runs under the road.

The problems began after completion of the £12 million Rookery Crossroads scheme in 2006, with an area of the road on the westbound carriageway near Two Mile Spinney repeatedly suffering subsidence.

The Highways Agency carried out a preliminary investigation to establish ground conditions and core samples were taken from the ground last year.

More extensive investigations involving CCTV and ground radar were conducted on the road in January, which revealed the cavities.

Brian Pitkin, route performance manager for the Highways Agency, said: "Since the subsidence first appeared, our main priority has been to keep the road open and safe.

"Identifying a long-term solution has proved to be particularly difficult.

"We appreciate the inconvenience this has caused and we ask for the patience of road users at this location."

David Ruffley, MP for Bury St Edmunds and Strowmarket, has written to the agency asking for a timescale of work.

He said: "I want these voids filled before the damaged road deteriorates further and causes an accident. I will continue to demand regular updates until this subsidence problem is resolved permanently."

A Highways Agency spokeswoman confirmed that interim works were likely to be carried out in March, but the final works had yet to be programmed.

"We are still looking at options for carrying out the final repair. We don't yet have a cost for repairs as design work isn't yet sufficiently advanced for us to be able to calculate this", she said.