The long-running saga over the construction of high-voltage power lines across the region took a new twist today as a landowner threatened fresh legal action.

Rosalind Craven has told National Grid and its contractors, Balfour Beatty, that they do not have permission to set foot on her land.

And Mrs Craven, of Home Farm, Huby, near Easingwold, North Yorkshire, said she was reserving the right to sue if there was any illegal entry.

She has received a letter telling her that Balfour Beatty wishes to enter her land at 1pm on Monday, initially for survey purposes and then to build an access track, foundations and three overhead pylons.

It is the latest in a series of disputes between objectors and National Grid over the controversial high-voltage power lines which are to be erected from Teesside to Shipton-by-Beningbrough, near York.

Mrs Craven has written to Balfour Beatty, asking: "Would you be good enough to forward to me unequivocal evidence demonstrating that you are legally and statutorily authorised to enter the farm on the day and time stated?"

She said she believed that the grant of a wayleave by the Secretary of State only authorised National Grid to install the line - and not its contractors.

She also believed it was possible neither National Grid nor Balfour Beatty had the necessary right of access, claiming National Grid had not gone through the necessary procedures back in 1991.

A National Grid spokesman said: "Regretfully, after years of negotiation, we now have no alternative but to gain access to the land under the legal rights granted to us in the necessary wayleave.

"We very much regret having failed to reach agreement with Mrs Craven and will take all reasonable steps to minimise any inconvenience or disruption caused by our construction activities."