Chancellor and health secretary are the first ministers to quit amid Tory unease over the Chris Pincher affair.
Shadow minister Sam Tarry has received support from Ed Miliband and Tulip Siddiq in his bid to remain Labour's election candidate in Ilford South.
One Conservative MP said: “It is clear from Lord McDonald’s letter today that Number 10 have not been honest in what they have said."
The MP was allowed to keep his job as a foreign office minister before going on to become deputy chief whip.
Downing Street confirms the prime minister was made aware of an investigation before appointing Pincher deputy chief whip.
His response even caused Newsnight host Kirsty Wark to look on in a brief moment of disbelief.
The former permanent under-secretary at the Foreign Office said No.10's various comments on the affair are "not true".
He also denied winking at Labour's deputy leader, saying the gesture was aimed at her colleague Ian Murray.
Simon McDonald disputes Downing Street’s account about what the prime minister knew about allegations surrounding Pincher.