David Cameron has confirmed that he would be prepared to withdraw from the European convention on human rights if a series of proposed changes to Britain’s human rights laws are rejected by Strasbourg.

The prime minister told the former Conservative chief whip Andrew Mitchell, a leading member of the “Runnymede Tories” who are committed to upholding British membership of the convention, that he rules out “absolutely nothing”.

No 10 later confirmed that Cameron remained committed to a policy document, outlined last year by former justice secretary Chris Grayling, to withdraw from the convention if parliament failed to secure the right to veto judgments from the European court of human rights.

Lord Falconer of Thoroton, the shadow justice secretary, warned that leaving the convention would inflict “incredible damage” to Britain’s standing in the world.

The prime minister clarified his thinking after Mitchell asked him to rule out withdrawing from the convention, which was drawn up by future lord chancellor David Maxwell Fyfe in the wake of the second world war to uphold human rights across Europe.

Mitchell said: “There is considerable concern on both sides of the house at the proposition that Britain might withdraw from the European convention on human rights. Will he take the opportunity today to make clear that he has no plans for us to do so?”

Cameron said he had no plans to withdraw from the convention but indicated that he wanted to keep the option in reserve if his proposals for change were rejected by the European court of human rights, which upholds the convention. The prime minister told his former chief whip: “Let me be very clear about what we want, which is British judges making decisions in British courts. And also the British parliament being accountable to the British people.

“Now our plans, set out in our manifesto, don’t involve us leaving the European convention on human rights. But let’s be absolutely clear. If we can’t achieve what we need – and I’m very clear about that when we’ve got these foreign criminals committing offence after offence and we can’t send them home because of their right to a family life – that needs to change. And I rule out absolutely nothing in getting that done.”

Michael Gove, the new justice secretary, is planning to implement two key manifesto pledges: scrapping the Human Rights Act and asserting the supremacy of the UK’s supreme court over Strasbourg. The move, which is designed to “break the formal link” between British courts and Strasbourg and to make the supreme court the “ultimate arbiter of human rights matters in the UK”, has been delayed until the EU referendum, which is due to be held by the end of 2017.

Senior Tories have also warned No 10 that Gove will face a crippling revolt unless he drops the “deeply offensive” threat by Grayling in his document last year to withdraw from the convention if the reforms are rejected by Strasbourg. No 10 confirmed that the Grayling document remained party policy. A spokesman said: “We have published a policy paper on this and that makes clear our view is that we are confident, we think we can get a better deal within the convention but we don’t rule anything out if that is not possible.”

Falconer said: “The prime minister raises yet again the spectre of leaving the European convention on human rights. Withdrawing from the convention would do incredible damage to the UK’s standing in the world and it is shocking that the government should dither over this issue.

“David Cameron and Michael Gove need to get their act together and tell us whether or not they intend to take us out of the convention. What is clear is that if they suggest scrapping people’s human rights protections, Labour will oppose them all the way.”

Meanwhile, the prime minister ame under pressure on his proposed renegotiations of Britain’s EU membership terms when the German vice-chancellor challenged his plans. Sigmar Gabriel, the economy minister in Germany’s grand coalition government, made his remarks after talks between centre-left leaders in Paris.

Reuters cited Gabriel as saying: “Our idea for Europe is quite the opposite of the idea of Mr Cameron. Mr Cameron wants to reduce Europe back to a single market. Mr Cameron wants to have a level playing field for companies but no level playing field for people. [Yet] Europe is made for people.”

Gabriel is chairman of Germany’s SPD party, which is more hostile to Cameron than the centre-right CDU party led by Angela Merkel. But senior CDU figures have voiced concerns in recent days about Cameron’s plans to demand a revision of the Lisbon treaty to underpin his proposed reforms.