Home Secretary David Blunkett has said he will look into Clare Short's claims that Britain spied on UN Secretary General Kofi Annan.
Several former ministers have criticised Clare Short
Mr Blunkett said he was "weighing up the detail" of her remarks before deciding if any action was needed.
She said she had seen transcripts of Mr Annan's conversations, but Mr Blunkett said he had not despite having access to more sensitive information.
Ms Short's colleagues accuse her of trying to undermine Tony Blair.
The former international development secretary has denied putting the UK or its security services at risk by saying Mr Annan's phone calls were bugged.
But Tony Blair, who branded the claims "deeply irresponsible", steered clear of the controversy during his speech to Labour's conference in Scotland and instead concentrated on the party's achievements.
Asked earlier if Ms Short's comments had breached the Official Secrets Act, Mr Blunkett said: "We are weighing the detail.
"Remember we don't have the facts that she's presented on the radio affirmed.
"We need to examine, in the clear light of day, what is required, what needs to be done and whether what Clare Short has said has said is in fact the truth."
Pressed about the transcripts she claims to have seen of Mr Annan's conversations, the home secretary said: "I wasn't shown any transcripts and I am one of the very few people - and Clare Short is not one of them - who have clearance for the full security material that comes through."
'Put up or shut up'
Mr Blunkett's remarks came after ex-foreign secretary Robin Cook said he "would be surprised" if it were true Britain had intercepted the calls of Kofi Annan during the run up to the Iraq war.
"This is part of Clare's political agenda to undermine the prime minister, and it is damaging both to the government and to the party which gave her all the privileges she enjoyed in government," he said.
"She should now put up or shut up."
But former UN Secretary General Boutros Boutros-Ghali said he had been warned his office and home would be bugged.
And Richard Butler, the former UN chief weapons inspector, claimed at least four countries bugged his conversations and he is convinced the UN's headquarters in New York is full of spies.
As a number of Labour MPs planned to table a Commons motion calling on Mr Blair to make a statement on the issue, Ms Short's former Cabinet colleagues criticised her outburst.
Ex-minister Jack Cunningham argued that Cabinet members had a duty to accept and comply with the obligations and privileges that came with their position.
"Clare Short obviously has a personal agenda which is to attack, damage and undermine the prime minister at every opportunity and sadly, that's been the hallmark of her conduct and behaviour since she left the government," he said.
Blunkett: Weighing up his options
Ex-Scotland secretary Helen Liddell said Ms Short's remarks were "completely unsubstantiated" and urged her to keep quiet.
"It is becoming increasingly difficult to work out where Clare is coming from. This is a pattern of behaviour that really is confounding her friends and colleagues and I don't think it is doing the country any good," she said.
Ms Short's former deputy, George Foulkes, said she had no evidence for her claims and the fisheries minister, Ben Bradshaw, accused her of impugning Mr Blair's integrity.
UN chief spokesman Fred Eckhard said any bugging would be illegal and should be stopped.