The union will be writing to the new prime minister today highlighting the unfair treatment.

“At a time when the government is seeking to further reduce severance terms across the civil service and the wider public sector, many people will find these double standards hard to stomach,” he said.

The Prime Minister sought to justify the additional payouts on the basis that advisers’ “employment is terminating more quickly than they had originally envisaged”.

Cameron also claimed that some of the special advisers had “…an expectation that their severance sum would be higher”.

Graham said: “Cameron clearly feels guilty that his staff are losing their jobs because of his failures. Perhaps he could explain why he didn’t make a special case for the thousands of civil servants who have lost their jobs since 2010 and left on reduced terms that were not as high as they expected?”