Sir Keir Starmer has been charged with weakening Britain's standing in the world by suggesting that the UN Security Council should have more permanent members.

According to Attorney General Lord Hermer, Britain will work to restructure the council by bringing in permanent representatives from Brazil, India, Japan, Germany, and Africa.

That would double the current permanent members, which comprises China, France, Russia, the UK and the US, although it also includes 10 non-permanent members who are elected for two-year terms by the UN General Assembly.

“We will advocate for reform of the Security Council, to ensure that those with seats at the top table truly represent the global community,” he said in a lecture to the Bingham Centre for the Rule of Law.

They mirror similar proposals advocated by James Cleverly when he was foreign secretary and called for reform of the UN Security Council.

The council is the UN body charged with maintaining international peace and security.It has responsibility for determining where UN peacekeeping troops should be deployed.

But Sir Iain Duncan Smith, former Tory leader, said it would be a mistake to widen membership further as it would be seen as a “dramatic weakening” of the UK’s foreign policy following the decision to hand over sovereignty of the Chagos Islands to Mauritius.

He feared it would play into the hands of Russia and China which have forged close relations with some of the proposed new permanent members. China has become India’s and Africa’s biggest trading partner and is increasing investment in Brazil, with financing for oil exploration and repairing railways.

Russia has sought to gain influence across Africa in recent years and has emerged as the security partner of choice for a growing number of African governments. India and Russia have forged a special relationship with increased cooperation across security, defence, trade, science and technology.

Sir Iain said: “China and Russia would be the net beneficiaries as they are hugely allied with the wider list of countries. With the exception of Germany that would be a disaster for the free world. It is utterly naive and dangerous.”

Grant Shapps, the former defence secretary, said: “First they surrendered the Chagos Islands in the British Indian Overseas Territory, and now they want to dilute Britain’s influence at the United Nations.

“When Sir Keir Starmer told us he’d bring change, he failed to mention it would involve shrinking Britain’s global responsibilities.”

Labour hit back at the criticism, pointing out that Mr Cleverly had advocated a similar expansion when he was foreign secretary, with the same countries.

A source close to David Lammy, the Foreign Secretary, said: “That was a government that Grant Shapps served in and he supported that policy. His comments are a bit absurd. They should have raised their objections to UK government policy when they were in government.”

General Kofi Annan, the UN Secretary, set out plans to increase permanent members of the Security Council in a 2005 report, In Larger Freedom. It set out two models. One added six new permanent seats and three two-year term elected seats. The second would create a new category of eight seats, renewable every four years.

However, reform has stalled because of the failure to secure agreement on which and how many countries could be added. Each of the five permanent members currently have a right to veto a resolution, unlike the 10 elected members who serve two-year non-consecutive terms.

Tim Loughton, former Conservative minister, favoured more fundamental reform of what was an “anachronistic” structure where just five members could veto motions that might be critical of one of them.

“Nobody is ever going to agree who the permanent members should be, in which case should we have any permanent members at all,” he said.