The interrogation of imprisoned IRA terror suspects was the subject of top level army and political debate in 1972, newly released papers reveal.
The Heath government introduced internment in Northern Ireland
Prime Minister Edward Heath, senior ministers and army officers were asked to define "interrogation-in-depth" by a Labour MP, George Cunningham.
Mr Cunningham wrote to Mr Heath to congratulate him on the dropping of some tactics such as hooding prisoners.
But the MP was concerned that other techniques of "pressurising" remained.
After the British government introduced internment - detention without trial - in Northern Ireland in 1971 a number of suspected IRA members were imprisoned.
Detainees thought likely to have important information were physically weakened through sleep deprivation and a bread and water diet.
Mr Cunningham expressed his concerns to the PM
They were then spread-eagled for hours against a wall with hoods over their heads and subjected to disorientating electronic white noise.
By 1972 the controversial techniques had been dropped, and in papers newly released by the National Archives, Mr Cunningham praised Mr Heath for the banning of "wall standing, hooding, noise, deprivation of sleep and semi-starvation".
But he added: "You said that these five techniques would be banned but that interrogation-in-depth would continue.
"Besides the doubt this has caused in my mind, I have had enquiries from some of the medical experts who gave evidence to the Parker Inquiry as to whether your replies mean that some techniques for pressurising prisoners will continue."
Mr Cunningham was Labour, later SDP, MP for Islington South between 1970 and 1983.
The Ministry of Defence (MoD) was asked to compose a reply, and one memo includes a note requesting "to see George Cunningham's letter to the PM, we are not entirely out of the woods yet".
Long Kesh internment camp in 1972
After much correspondence between ministers and civil servants, it was decided that interrogations would be based on civil police practice.
In one memo Mr Heath also says that if any new interrogation techniques were to be brought in it "would mean that the government of the day would almost certainly have to seek the authority of Parliament".
The Irish government made a formal complaint to the European Commission for Human Rights and later the European Court of Human Rights, about the controversial interrogation techniques.
The Commission found Britain guilty of torture, but the European Court ruled the treatment was inhuman and degrading but did not constitute torture.