In a letter to army veterans published by BBC News, Ms May said the UK government is “concerned that the whole system of addressing the past in Northern Ireland is unbalanced and is not working well in anyone’s interests”.

She added: “That is why we agreed with the Northern Ireland political parties, in the Stormont House Agreement in 2014, to establish new institutions that would investigate the past in a way that is fair and proportionate.

“The overwhelming majority of deaths caused by soldiers and police officers will have been lawful and it is essential that investigations into the past do not unfairly treat soldiers and police officers.

“Establishing these new institutions will ensure that the focus of investigations will be much more on the hundreds of unsolved murders committed by terrorists, including many unsolved murders of soldiers and police officers.”

Her comments echo those by Northern Ireland Secretary James Brokenshire, who has previously criticised “the imbalance of the current system of legacy investigations”.

Mr Brokenshire has lent credence to allegations there is a “disproportionate” focus on prosecuting former British soldiers.

That view has been strongly rejected by the Public Prosecution Service for Northern Ireland (PPS), while Northern Ireland’s former Justice Minister David Ford said Mr Brokenshire had come “perilously close to interfering in the rule of law”.

Northern Ireland’s Director of Public Prosecutions, Barra McGrory QC, has said the PPS “have prosecuted more legacy cases connected with paramilitary cases than we have in respect of military cases”.