The development is part of Milton Keynes City Council’s Local Plan 2050, external, but would be the first project to spill over the local authority’s boundary.

Hallam Land said it was hosting three consultation events on the proposals over the next two weeks, and hoped to put an outline planning application to the city council later this year.

Clark said there was an “important principle at stake here”.

“If this is granted planning permission, it would be the start of the expansion of Milton Keynes into Central Bedfordshire, and I will be calling on Central Bedfordshire Council to resist,” she said.

Hallam Land said it was committed to working collaboratively with both councils.

Spokesperson Peter Glazebrook said: “We are committed to bringing forward an application which offers the homes, jobs and infrastructure to benefit future generations.”

The government has recently rejected a fast-track devolution deal that could have involved several councils, including Central Bedfordshire and Milton Keynes.

However Clark said she remained wary of the long-term implications, if those plans return to the table and mean both councils are incorporated into a larger combined authority.

“If we find ourselves part of the Government’s devolution plans with Milton Keynes, then I suspect this will only be the start,” she said.

Adam Zerny, independent leader of Central Bedfordshire Council, said: “We understand the developer wants to build on land in the Milton Keynes area, and some in Central Bedfordshire and we would expect to work closely with Milton Keynes over any border issues as has been the case in the past.”

Milton Keynes City Council said it would not comment due to the ongoing consultation by the developers.