A senior civil servant in the department of transport broke with tradition yesterday when he released a statement detailing the events leading up to the resignations of communications director, Martin Sixsmith.

Sir Richard Mottram attempted to exonerate transport secretary Stephen Byers when he claimed that Sixsmith had agreed to resign.

In a four page statement, the mandarin claims that Sixsmith made three conditions to his resignation - that Jo Moore also resign, that he was not blamed and that the financial terms of his leaving were agreed.

In the statement, Mottram conceded that the news of Sixsmith's departure was leaked, meaning that no such terms were arranged at the time.

Sixsmith, however, still challenges the claims, insisting that at no time did he formally agree to quit.

Calls from the Conservatives for Byers to resign were supported by the Liberal Democrats and the Scottish National Party, however Downing Street continued to support the transport secretary.

Whilst Downing Street remained vague on Byers' involvement in the decision to force out both Moore and Sixsmith, a spokesman insisted that the minister still had the "full support" of the prime minister.

MPs are now calling for a Civil Service Act, to enshrine in law the impartiality of the service.