Kenneth Clarke, the former justice secretary, has lambasted Tory plans to ensure that rulings by the European court of human rights (ECHR) are no longer enforceable in the UK, warning that future governments could make arbitrary decisions.

Clarke said he was astonished by government proposals to withdraw from the European convention on human rights if its reforms were rejected.

He told The World at One on BBC Radio 4: “I am rather bewildered by it all. As I understand it we are anxious to comply with the European convention of human rights and quite happy to accept the judgments of the European court of human rights unless the government of the day has a whipped parliamentary majority to reject the judgments that we don’t approve of. I find that rather bewildering.

“For the good of our society I don’t think that the executive of the day should be exempt from having to comply with judgments. Sooner or later, if we allow our standards to slip, some arbitrary decision will take place.”

Clarke, who retired in the summer reshuffle, spoke out after Chris Grayling, the justice secretary, said a Tory government would withdraw from the convention if parliament failed to secure the right to veto judgments from the ECHR. A withdrawal from the convention could jeopardise Britain’s membership of the EU, which is separate to the Council of Europe – whose members are drawn from across the continent and include Russia and Ukraine. EU member states must be in the Council of Europe.

Clarke warned that the changes could encourage the Russian government to ignore the judgments of the court. He said: “I am sure [Russia] would welcome the idea that the Duma could set them all aside. But so far they haven’t been able to win that concession.”

Under the proposals to be included in the party’s general election manifesto, the Tories would reverse more than half a century’s tradition of human rights authority residing in Europe. The authority of the court in Strasbourg would be severely curtailed, with parliament given the final say on whether or not to adopt ECHR decisions.

Asked on BBC Radio 4’s Today programme whether he would be prepared to withdraw from the convention, Grayling said: “If we cannot reach agreement that our courts and our parliament will have the final say over these matters then we will have to withdraw.

“We have a treaty right to withdraw, it is specifically provided for in the convention. We would exercise that right. There is always a first time for everything.”

A withdrawal from the convention could also place Britain in breach of its international obligations in the 1998 Good Friday agreement, which helped to bring peace to Northern Ireland. The agreement, which was approved by referendums on both sides of the Irish border and lodged at the UN, said the two communities in Northern Ireland would be protected by safeguards that include “the European convention on human rights and any bill of rights for Northern Ireland supplementing it, which neither the assembly nor public bodies can infringe”.

In its first – and damning – response to the proposals a spokesperson for the Council of Europe, said they are inconsistent with membership.

The brief statement issued by the council highlights article 46 of the convention , which states that the countries contracted into the agreement “undertake to abide by the final judgment of the [ECHR in Strasbourg] in any case to which they are parties”.

The Council of Europe statement says: “We take note of these proposals by the Conservative party. We also take note they are not draft legislation. As they stand, the proposals are not consistent with the [European convention on human Rights].”

Dominic Grieve, the former attorney general who was removed at the last reshuffle, told the Guardian the proposals were “almost puerile”. He added: “I also think they are unworkable and will damage the UK’s international reputation.”

The proposals also drew a furious response from the Tories’ coalition partners. Simon Hughes, the Liberal Democrat justice minister, said: “The Conservatives don’t care about the rights of British citizens – they care about losing to Ukip. These plans make no sense: you can’t protect the human rights of Brits and pull out of the system that protects them.

“Europe’s human rights laws were designed by British lawyers to reflect British values of justice, tolerance and decency. We will not allow the Tories to take away the hard-won human rights of British people when in the UK or anywhere else in Europe.”