DAVID Cameron has rejected Nicola Sturgeon's call for pre-election talks with the civil service on the SNP's policy priorities.

Officials traditionally meet opposition politicians who could form the next government to prepare for a possible change in administration.

Senior Whitehall staff began discussions with Ed Miliband's Labour party months ago.

But the Prime Minister has refused to allow civil servants to enter discussions with the SNP or any of the other smaller parties who could hold the balance of power in May.

In a letter to the First Minister Jeremy Heywood, the UK's top civil servant, said that Mr Cameron "does not want to extend the offer more widely to parties, for example, that are fielding candidates in only some parts of the country".

SNP sources denounced the Prime Minister's decision as "undemocratic".

One said: "This is extremely disappointing by David Cameron - we are taking nothing for granted, but all the polling evidence indicates that the SNP could be in a powerful position on behalf of Scotland in the next Westminster parliament, and we should be treated equally on that basis.

"That would be fair to voters not just in Scotland, but across the UK."

Ms Sturgeon's call was backed by a number of other parties including Plaid Cymru, the DUP and Ukip.

Before the 2011 Scottish Parliament elections, pre-election talks were authorised between civil servants and all of the Holyrood parties.

Ms Sturgeon had argued that with polls pointing to a hung parliament in May, Westminster's smaller parties may be in a position to demand some of their policy objectives as the price of propping up a government.

She said last month: "The SNP programme includes a substantial alternative to the austerity cuts supported by the UK Westminster parties, cancelling the renewal of the Trident nuclear weapons system, and a requirement that each and every constituent nation of the UK would have to vote to leave the European Union in any in/out referendum before the UK could exit.

"These and other policies which we will seek to advance in the next parliament are obviously of UK-wide application, and I believe that the Whitehall system would benefit from becoming more familiar with our propositions."

In his letter Mr Heywood confirmed that the issue was a "matter for the Prime Minister".

He added that last year Mr Cameron had agreed to talks with Labour.

"With less than a month now to the dissolution of Parliament he does not want now to re-open that decision and extend the offer more widely to parties, for example, that are fielding candidates in only some parts of the country," he said..

"It would of course be important for the civil service to maintain an awareness of the main policy objectives of the minority parties in case discussions become relevant in the post-election period, should there be a hung parliament.

"I can assure you we will be doing this."