Flouting European judges over prisoner voting would risk international “anarchy”, the Government’s chief law officer has warned.
Attorney General Dominic Grieve, above, said sticking to international rules could be “irksome” at times.
But it had been the “settled view” of British governments for centuries that such obligations should be met.
The intervention came in evidence to the parliamentary Joint Committee on prisoner voting.
The MPs and peers are considering how to respond to a European Court of Human Rights ruling against the UK’s blanket ban on convicted prisoners taking part in elections.
David Cameron has said that the idea of overturning the ban makes him “physically sick”, and the Commons overwhelmingly rejected the prospect in an indicative vote.
The committee has been asked to consider three options for a draft bill: giving the vote to convicted prisoners serving up to six months, giving it to those serving up to four years or keeping the existing blanket ban.
Mr Grieve said parliament had the power to withdraw from the European Convention on Human Rights, or any other commitment.
“Many of these international legal obligations, they impose obligations on others which we think benefit the international order and indeed us,” he said.
“But at the same time they may at times impose obligations on us.
“That obligation may at times be irksome.
“You can always withdraw from an obligation by leaving a treaty or denouncing it.
“But while you are adhering to it, it seems to me that one has to think very carefully about what the consequences are in deciding that you can cherrypick the obligations that you are going to accept.
“Whilst it may be perfectly possible to disregard them you are creating a degree of anarchy in the international order that you are trying to promote.”
The Tory MP and QC – who personally argued the Government’s case to the court – said it would be “no slight matter” to ignore the ruling.
“You can’t expect to be able to get other countries to observe international legal obligations if you choose not to,” he said.
Thorbjorn Jagland, Secretary General of the Council of Europe, told the committee it would be impossible for the UK to leave the convention on human rights and remain a member of the council.
He warned that Britain’s international influence would be diminished if it decided to go for the “nuclear possibility” of not complying with the ruling, and the whole ECHR system would be compromised.
“The implications for the Council of Europe would be… that other countries will start to do the same and it will be the beginning of the weakening of the whole convention system,” he said.
“If one says that we can pick and choose the judgments that we want to execute, then others will say exactly the same and then this convention will be another convention, for instance like they have in the United Nations.
“They are very weak.
“They are there but there is no enforcement of the standards.
“If you start to pick and choose the judgments from the court of course the court will be weakened and in the end have no meaning.”
Mr Jagland added: “The impact for Britain as I see it would be negative.
“It would harm UK reputation and influence in Europe and in the world.
“Can you imagine what would happen if the UK as the founding father of this institution is to leave it?”
Mr Jagland said: “Europe cannot afford to let the UK leave the whole convention system, which is so important.
“None of us should put that to the (test).
“We should try to avoid it.”
The strength of the ECHR was that individual citizens from member states were able to petition it on points of law, he said.
Mark Leech editor of Converse the national newspaper for prisoners in England and Wales said the issue of prisoner voting brought into focus the sharp distinction between political reality and rhetoric.
Mr Leech said: “Politicians of every colour continually tell us they want to reduce reoffending, they want to help those in prison to lead law-abiding lives both in custody and after release, in fact there is a large notice to that exact effect pinned to the front gate of every prison in the country.
“And yet, when you try and see the translation of that theory into practice it falls at the first hurdle by refusing prisoners the ability to vote, excluding them from society, refusing to follow the judgment of the highest human rights court in Europe, a court the UK has signed up to and in which we played a central part in creating – criminal justice policies on rehabilitation are, sadly, shown to be nothing more than a sham.”