The SNP have hit out at David Cameron after Downing Street suggested that the party was not important enough to warrant pre-election talks with the civil service.
No 10 said that official discussions were held only with the "principal opposition parties".
The Prime Minister's official spokesman later clarified that meant only to those parties which stand candidates across the UK.
The row came after Mr Cameron barred the SNP from entering talks with the civil service ahead of polling day.
Whitehall officials traditionally meet opposition politicians who could potentially form the next government to prepare to implement its manifesto.
With polls suggesting a hung parliament in May the SNP, and a number of other smaller parties, argues it has a strong chance of seeing some of its policies implemented.
SNP Westminster leader Angus Robertson accused Mr Cameron of "the height of hypocrisy".
"He reluctantly accepts the SNP should be included in TV debates because he wrongly thought it might help him avoid them.
"But he refuses to offer us pre-election access to the civil service to discuss our progressive policy agenda," he said.
He added that in a hung parliament the SNP "could well be in a position of influence in terms of how the UK as a whole is governed, and therefore it is in people's interests north and south of the border for us to be included in access to the Whitehall civil service."
Talks with Ed Miliband's Labour party months ago, on the instruction of Mr Cameron.
But the Tory leader has blocked similar negotiations with the SNP and other small parties, including including Plaid Cymru, the DUP and Ukip.
In a letter to the First Minister this week, seen by The Herald, 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 described the Prime Minister's decision as "undemocratic".
The Prime Minister's official spokesman said that it was a "long-standing position that discussions are held with the principal opposition parties".
He later made clear he was talking in terms of the UK as a whole.
In the run up to the 2011 Holyrood election talks were held between civil servants and all of the Holyrood parties.
Those discussions were authorised by then First Minister Alex Salmond.
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