The leases on hundreds of homes on Newmarket's Studlands Park and in Soham will be terminated in December by builder Persimmon Homes, which wishes to concentrate its efforts on building new houses, such as 150 earmarked for Skeltons Drove, in Beck Row.

A spokeswoman for the two air bases said: "Some people have expressed concerns because they have to move. We recognise the hardships these situations may cause, but we are working closely with everyone involved to mitigate them and make their transition as smooth as possible."

She added that US government housing was available at RAF Mildenhall, RAF Lakenheath and RAF Feltwell, but families would have to be placed on a waiting list. Otherwise they would have to look towards private letting agents to find a home, added the spokeswoman.

Andrew Fuller, deputy managing director at Persimmon Homes Anglia, confirmed that the company's involvement in these housing areas would cease at the end of the year.

He said: "All properties will be handed back to the various owners. However, I am aware that a number of owners are hoping to continue a lease arrangement with the USAF and are therefore in discussions directly which we are not party to."

He added: "At Persimmon, we wish to concentrate our time and resources on our core businesses, ie new build residential properties, and with this in mind our new development at Beck Row will commence in the next few weeks."

The 150 homes due to be constructed can only be occupied by USAF personnel.

The planning condition was agreed by Forest Heath District Council, which granted final permission for the project in November. Mr Fuller hopes that the first properties on the site will be complete by December.

Some families in the Lords Walk housing area, near Eriswell, will also have their leases reviewed when it re-opens to the public at the end of May.

Last summer, work began to move a checkpoint at RAF Lakenheath's Gate 2 eastwards along Lords Walk, and to construct a new perimeter fence along Radcliffe Road.

Around 600 base homes in that area will be officially classed as off-base when the new check-point opens.

A spokeswoman for RAF Lakenheath said the only immediate difference to personnel was they would have to show their identification cards to gain access to the base.

She added that lease discussions with the USAF and house owners were under way.