Penny Mordaunt has backed the prime minister as Theresa May faces a confidence vote from Conservative MPs.
A vote is to take place tonight after 48 MPs called for Mrs May to go in letters to Sir Graham Brady, chairman of the backbench 1922 Committee.
The secret ballot, to be held between 6pm-8pm, will see Tory MPs vote on Mrs May’s future as leader of the party.
But Penny Mordaunt, Portsmouth North MP and international development secretary, posted on Twitter and said: ‘The Prime Minister has my full support, not least because she has always done what she firmly believes is in the national interest.
‘Our country needs us all to fight for a good deal and prepare for a no deal scenario.
‘All eyes and hands should be on that task.’
Speaking this morning in Downing Street, Mrs May said she would fight the confidence vote ‘with everything I've got’ and would ‘finish the job’.
But Stephen Morgan, Portsmouth South MP, has hit out at ‘panto politics’.
In a statement he said: ‘Last week Theresa May’s team was unprecedentedly found in contempt of parliament. Now the PM’s own party may sack her.
‘The last thing the country needs now is more uncertainty. This is another example of the interests of the country being overlooked in favour of games, panto politics and childish squabbles.
‘The government need to be putting the country first and providing real leadership at this time of constitutional crisis. Portsmouth people and our country deserve better than this current government.’
West Meon MP George Hollingbery, who represents Waterlooville, said if Mrs Day’s withdrawal deal is not supported ‘we run the risk of reneging on the referendum’.
He said: ‘I will support the Prime Minister in today’s vote without hesitation. She has worked tirelessly in incredibly difficult circumstances to secure an EU withdrawal deal that delivers on Brexit - ending free movement, gaining control of our laws and seas and leaving the single market.’
‘No-one will secure a better deal than the one the Prime Minister has negotiated and a change of leader now will either delay or stop Brexit and makes absolutely no sense.
‘We must be clear here: the only alternative is a no deal Brexit that will harm jobs and livelihoods across this country. That is an option I cannot countenance and the parliamentary party should not either.’
In a statement Sir Graham said: ‘The votes will be counted immediately afterwards and the result will be announced as soon as possible in the evening.’
It comes as the government pulled a House of Commons vote on the Brexit withdrawal deal, which Mrs May was widely expected to lose.