Britain will protect its armed forces serving overseas from "vexatious" human rights claims by making it possible to suspend the European Convention on Human Rights in future conflicts, Prime Minister Theresa May said on Tuesday.

The ruling Conservative Party has criticised what it calls spurious legal claims against British troops returning from war, especially from Afghanistan and Iraq, and the government has said it has spent millions of pounds on failed cases.

"Our armed forces are the best in the world and the men and women who serve make huge sacrifices to keep us safe," May said in a statement.

"We will repay them with gratitude and put an end to the industry of vexatious claims that has pursued those who served in previous conflicts."

The statement said the introduction of "a presumption to derogate" from the ECHR, subject to the circumstances at the time, would protect British troops serving in future conflicts from "the kind of persistent legal claims that have followed recent operations in Iraq and Afghanistan".

May, who said on Sunday she would trigger the procedure for Britain to leave the European Union by the end of March, has stamped her authority on her government since being appointed prime minister shortly after the June EU referendum.

Her predecessor, David Cameron, had pledged to defend the armed forces from legal claims, many over alleged abuse since British troops were involved in the US-led invasion of Iraq in 2003. Lawyers say many of the cases were proven.

Since 2004, Britain's defence ministry has spent more than £100 million on Iraq-related investigations, inquiries and compensation, the statement said.

"Our legal system has been abused to level false charges against our troops on an industrial scale," defence minister Michael Fallon said in the statement.

"It has caused significant distress to people who risked their lives to protect us, it has cost the taxpayer millions and there is a real risk it will stop our armed forces doing their job."