The IRA planned to knock out the power supply to the south east of England in the final years of its bombing campaign, a former insider has claimed.
Details are revealed in the final episode of the BBC series Spotlight on the Troubles: A Secret History.
Insiders describe a battle of wits between the IRA and British intelligence.
When the British Government refused to admit Sinn Féin to peace talks in the mid-1990s, Canary Wharf was bombed.
Two people were killed and damage was estimated at £150m in the attack in February 1996.
In June of the same year, the IRA exploded what was reported as the largest bomb to be planted in Great Britain since World War Two.
More than 200 people were injured in the blast in Manchester and significant damage to infrastructure caused.
The final programme in the landmark BBC series, presented by Darragh MacIntyre, includes first-hand accounts of the campaign in Britain after the IRA ceasefire was temporarily abandoned in 1996.
But the programme reveals how key IRA bombers were caught or killed after extensive surveillance operations by British police and MI5.
Former US Marine John Crawley, who had already been caught smuggling guns from America for the IRA, was arrested just before he could bomb London’s electricity supply.
“We were going to knock out the power supply of the south east of England,” he tells the programme.
“There may have been other operations after that, but we were caught before we could do that.”
John Grieve, who took over Scotland Yard’s anti-terror unit on the day of the Canary Wharf bomb, tells Spotlight that Crawley and the other IRA bombers were “the A team”.
“They were absolutely excellent and one of them, John Crawley, ex-US Marine Corps demolition specialist, this was the top sort of people for them to bring up.
“He just epitomised the cunning, skills, experience of the sort of people they were putting against us.”
But Mr Crawley reveals that the IRA was stretched by the bombing campaign by the time he was arrested in 1996.
“I wondered why they didn’t kill us, because we’d have had men tooled up and everything,” he says.
“They knew where we were going and to this day, I don’t know why they just didn’t take us out of it because coffins coming back on the ferry would’ve been a nice message to anybody else looking to go.
“And believe me, there wasn’t a lot of people putting their hands up to go to England.”
The final episode will be broadcast on Tuesday 22 October on BBC One NI and BBC Four at 20.30 BST.
Following this broadcast, a programme looking at the making of the series will be available to view on BBC iPlayer.
Spotlight on The Troubles: Behind The Scenes will also be shown on Thursday 24 October on BBC One NI at 21:00.
Following the broadcast of the final episode, the series – presented by Mandy McAuley, Jennifer O’Leary and Darragh MacIntyre – will be available as a box set for up to a year on BBC iPlayer.
Spotlight on The Troubles: A Secret History can be viewed on BBC iPlayer here