Penny Mordaunt took aim at her ministerial boss by joking she was “amazed” to be back at the Commons despatch box given her “reported work ethic”.

Supporters of the trade minister also lavished praise on her as she returned to her frontbench duties in the House after being knocked out of the Conservative Party leadership race.

Her comments came after International Trade Secretary Anne-Marie Trevelyan criticised Ms Mordaunt during the contest, saying: “There have been a number of times when she hasn’t been available, which would have been useful, and other ministers have picked up the pieces.”

Ms Mordaunt also used trade questions to confirm the UK is negotiating with 25 of the 50 American states in a bid to agree economic pacts.

Tory former minister Dame Andrea Leadsom, a key backer of Ms Mordaunt, told the minister: “Can I pay tribute to my right honourable friend for a fantastic and brave and clean campaign for the leadership of the Conservative Party and to be prime minister.”

She asked: “Does she agree with me that being a force for good in the world for free trade is an absolutely honourable goal and one that the UK should be promoting every chance we get?”

Ms Mordaunt, MP for Portsmouth North, responded: “Yes, I am sort of amazed to find myself here this morning given my reported work ethic. But I am here.

“And she is absolutely right. Us, a G7 nation, leaving the regulatory orbit of the EU is an international event. And it gives us huge opportunity, but also nations like the United States, to really set out our view of the world and capitalism and fight for those things that we believe in.”

Ms Mordaunt aimed a further dig at Ms Trevelyan after Labour criticised the Department for International Trade for a “truly shameless attempt” to “dodge any form of scrutiny” over the UK-Australia free trade agreement.

Shadow trade minister Ruth Cadbury said the department had “swerved” eight invitations to attend the Commons International Trade Committee and had avoided holding a vote on the deal ahead of its ratification.

Ms Trevelyan was accused earlier this week of having “bottled” appearing before MPs to discuss the deal.

Ms Mordaunt, in her reply, said: “For my own part, every single time the International Trade Committee or other body of this House has asked me go before it, I have.

“I think that’s the attitude of the ministerial team and we will continue to do that.”

Shadow international trade secretary Nick Thomas-Symonds said: “I welcome the Member for Portsmouth North back after her efforts in the Tory leadership contest.

“But the Secretary of State is far less complimentary about her efforts in the department.”

Mr Thomas-Symonds went on to read out the criticism made by Ms Trevelyan.

As Tory MPs aimed shouts of “shameful” at him, he pointed out: “They shout ‘shameful’ at me – these are the Conservatives’ words about each other, not my words.”

Ms Trevelyan replied: “I have a fantastic team of ministers, which is exactly why we’re able to do all we can to make sure that our UK businesses have access to UK support and Government support to get their fantastic goods and services across the world.”

Conservative Alicia Kearns (Rutland and Melton) said of Ms Mordaunt: “I’ve always been struck by the Member for Portsmouth North’s quiet diligence in doing her job.

“So can she please update me on the progress of signing individual deals with US states, which my farmers in Rutland and Melton are particularly interested in.”

Ms Mordaunt replied: “This week we have continued our negotiations with Utah, and yesterday we also signed the second state level MOU (memorandum of understanding) with North Carolina, which will be based on green growth.

“We are currently negotiating with half of all US states.

“The first eight deals we will sign will be covering 20% of the US economy and this will open up procurement, enable mutual recognition of qualifications, and enable British businesses to take a larger share of both goods exports and also exports of services.”

Conservative former minister Tim Loughton noted Ms Mordaunt is “allegedly work shy” as he praised her work with the American states, joking: “Think what she could achieve if her focus was on the job.”