Former DUP leader Ian Paisley said he was “very angry” when he learned of the deaths of 13 unarmed civilians, later 14, on Bloody Sunday in Derry in January 1972. In particular he condemns what he calls “the attempt [by the British] to cover it for what it was not”.

He tells journalist Eamonn Mallie in an interview on BBC: "The inquiry afterwards proved that some of these people had neither weapons, nor were they using weapons."

He commends prime minister David Cameron for setting the record straight in the House of Commons and apologising for the deaths: "Well, I wasn't embarrassed. I was glad to hear him for the first time as a British leader telling the truth about it. Saying what really did happen."

His remarks are to be broadcast in a two-part interview on BBC One Northern Ireland beginning on Monday. Two hours of interview material will be shown, but some 40 hours were recorded.

Dr Paisley (87) appears in robust spirits and good voice. The first candid interview dwells on the early years of his political career and clerical ministry. He is typically forthright in his criticisms of former leaders – Stormont prime minister Capt Terence O'Neill, former British prime minister James Callaghan, Northern secretary Roy Mason and, particularly, Margaret Thatcher.

He accuses her of "betrayal" over her work with taoiseach Charles Haughey on the "totality of relationships" between Ireland and Britain and because of her signing the Anglo-Irish Agreement in 1985 formally giving Dublin a consultative role in the North. "I thought she would be a good friend to Northern Ireland, but I was sadly disappointed," he admits.

Referring specifically to the Anglo-Irish Agreement, Dr Paisley brands it “a surrender document”.

"Even very mild unionists would agree with that. It did unite the unionist people. For the first time I could sit in company with Ulster Unionists who saw the same way as I was seeing."

He contends that the then DUP deputy leader Peter Robinson was wrong to invade the Border village of Clontibret, Co Monaghan. In protest at the alleged poor state of Border security in the wake of the Anglo-Irish Agreement, Mr Robinson led an "invasion force" of 500 across the Border to Clontibret to allege how lax security measures were. The local Garda station was attacked and Mr Robinson was later fined.

Dr Paisley was out of the country at the time and now makes clear his dim view of the episode and Mr Robinson’s role in it. “He did it and he must take account for it,” Dr Paisley says of his former deputy.

Paisley: Genesis To Revelation. Face To Face With Eamonn Mallie; BBC One Northern Ireland, next Monday, 10.35pm