Celtic manager Neil Lennon, QC Paul McBride and former MSP Trish Godman targeted with letter bombs

• Celtic manager Neil Lennon, QC Paul McBride and now retired Labour MSP Trish Godman

Celtic manager Neil Lennon, his QC Paul McBride and the politician Trish Godman, a Celtic supporter, were each sent a package containing improvised explosives with the power to kill or severely wound the recipient.

A team of Strathclyde Police officers are now hunting the bomb-maker, who sent the packages to his intended victims at a time when Old Firm sectarian tensions are running high.

The Scotsman understands that all three bombs were intercepted by the Royal Mail or the police before they reached their intended victims, all of whom are Catholics. It is understood the devices, which may have been made by someone with a military background, were home-made and crude, but nonetheless could have killed the recipients if they had exploded when opened.

The letter bomb plot has been under intense investigation for nearly a week by the police and the destruction it could have wrought, as well as the heightening of sectarian tensions ahead of Sunday's game between Rangers and Celtic, have caused grave concern at the highest levels of the Scottish Government.

After being given the details, First Minister Alex Salmond convened a secret Cabinet meeting on Saturday night to discuss the situation. High-level discussions have also been taking place between the First Minister and the police about the matter, which has only now be made public.

Mr Salmond said last night: "We will not tolerate this sort of criminality in Scotland, and as an indication of the seriousness with which we view these developments the Cabinet sub-committee met last Saturday to ensure that the police investigation has every possible support to come to a successful conclusion. We are confident that this will be the case."

Last night, former Celtic director Michael Kelly said he was shocked by the turn of events.

"This goes well beyond football and this goes well beyond sectarianism," he said.

"This is terrorism and should be treated as such. We have seen the First Minister call a summit to deal with minor scuffles and claiming successes. But this is actually an act of terrorism – it is political or religious, and this is certainly not football supporters doing this for football reasons."

Lennon has already been the subject of several death threats. The Celtic manager is now under police guard and is said to have a panic button installed in his house. Early last month, police discovered a fake nail bomb and bullets that were intended for the Celtic manager.

Last night, however, it emerged that he was sent a bomb at the end of March that had the potential to kill. A similar device was sent to Mr McBride, the outspoken lawyer who has been acting for Lennon and has accused the Scottish Football Association of being biased towards Rangers.

A third bomb was sent to Mrs Godman, a deputy Presiding Officer in the last Scottish Parliament, who is a Celtic supporter but has had no involvement in recent controversies that have dogged the Old Firm fixture.

The Scotsman understands that she was targeted because she wore a Celtic strip on the day that the Holyrood Parliament broke up for the election.

"We believe she wore a Celtic top to the last day of parliament," a police source said last night. "I know you shouldn't differentiate between the bombs, but the Trish one just shocks. It is just outrageous."

The bomb sent to Lennon was picked up by the Royal Mail on 26 March in the Kirkintilloch sorting office. At first it was thought to be a fake, similar to the one discovered on 4 March in the Saltcoats sorting office.

But after further tests were carried out on the second bomb, it was found to be a viable device with deadly potential.

Two days after police were alerted to the bomb at Kirkintilloch, they intercepted a similarly device that had been delivered to Mrs Godman's constituency office in West Renfrewshire. Mrs Godman has just retired from parliament after spending the past decade as a Labour MSP.

The most recent bomb, addressed to Mr McBride at the Faculty of Advocates, was picked up on Friday before it could reach its destination. A source close to Mr McBride said: "He was appalled at someone behaving in this fashion and he had nothing but praise for the way the police have conducted this very difficult inquiry."

Police believe one person was behind the attacks. Although they have not ruled out the suspect having some military experience, the devices are not thought to have been the work of a seasoned terrorist.

"The bottom line is that they could have killed someone," said a police source.

With another Old Firm match scheduled for Sunday, police are today expected to appeal for calm when they host a morning press conference to release details of the attacks.

A source said: "One would hope that sensible voices are going to say that this has got well out of hand.

"We have got a bunch of resources on this. An investigation like this has a lot of people working on it."

Scottish Labour Leader Iain Gray said: "I am shocked and appalled at this sinister development. It is vital, though, that people keep calm and do not let the situation spiral out of control as that would be playing into the hands of the extremists behind this vile act."

Sectarian tensions erupted last month after a Scottish Cup replay that saw Lennon and Rangers assistant manager Ally McCoist clash on the touchline. Police arrested 187 people for disorder before, during and after the match. Another 40 were arrested for domestic abuse.

After the managerial altercation, Lennon, who already had misconduct offences this season, was given a touchline ban for four matches.

McCoist was given a two-match touchline ban, which he later successfully appealed. Rangers players Madjid Bougherra and El-Hadji Diouf were given red cards during the quarter-final replay.

After McCoist won his appeal against his ban, Mr McBride said: "The SFA have been shown to be not merely dysfunctional and not merely dishonest, but biased."

In reply, the SFA chief chief executive, Stewart Regan said: "Paul McBride's wild and inaccurate statements are defamatory. The Scottish FA is now considering whether to sue."