West Midlands Police have denied using a stun gun on a suspected suicide bomber was an unnecessary risk.
A Taser gun was used to arrest bomb suspect Yasin Hassan Omar
A Taser device was used during the arrest of the 21 July failed Tube bombings suspect Yasin Hassan Omar.
Metropolitan Police Commissioner Sir Ian Blair said officers using a Taser on a suspected suicide bomber ran an "incredible risk" of detonating a bomb.
But West Midlands Police said Sir Ian did not know the full circumstances surrounding the arrest.
Sir Ian told BBC One's Questions of Security programme: "We use Tasers in London regularly, but a Taser sends electric currents into the body of somebody.
"If there is a bomb on that body, then the bomb is going to go off.
"It may have been that they [officers in Birmingham] were clear there wasn't a bomb. I don't know what the situation was."
Sir Ian said his officers had, tragically, been left with no choice but to open fire on a Brazilian man wrongly suspected of being a suicide bomber.
Jean Charles de Menezes, 27, was shot dead at Stockwell Tube station on 22 July.
Sir Ian said using a Taser in such a situation was "not an option".
He was "devastated" for Mr Menezes' family but stood by the force's shoot-to-kill policy for suspected suicide bombers.
"There is only one way to stop someone who is a suicide bomber which is to kill that person."
West Midlands Police said in a statement that Mr Menezes' shooting and Omar's arrest "may appear similar but they were separate incidents".
"The information and intelligence would have been different, the threat level to officers and the public was different."
"Every situation in which firearms are deployed is unique."
West Midlands Police have voluntarily referred the use of the Taser to the police watchdog, the Independent Police Complaints Commission (IPCC), for investigation.
The IPCC have also launched a witness appeal at Stockwell station.
Edgware Road station opened for the first time since 7 July
Chairman Nick Hardwick said the Home Office should stop issuing "partial information" and "people" should "shut up" until his independent investigation had established the facts.
On Thursday, the Home Office said Mr Menezes' visa had expired two years before he was shot by police.
A passport stamp apparently giving him indefinite leave to remain "was not in use" on that date, added officials.
The Home Office said it wished to end speculation over his immigration status, but said the statement was not intended to influence any investigations.
Mr Menezes will be buried in his home town of Gonzaga in the south-east of Brazil on Friday.
Menezes family spokesman Asad Rehman told BBC News they and "all the people of London and Britain want to see the truth of why this death took place".
Mr de Menezes' funeral will take place in his home town on Friday
In other developments:
Edgware Road station has opened for the first time since the 7 July bomb attacks.
The Rail Maritime and Transport union (RMT) - the biggest trade union for Tube workers - is calling for more rail guards on trains and better emergency training and equipment, including breathing apparatus for rail staff.
Nine men were arrested by police in Tooting, south London, on Thursday, bringing the total number of people held under anti-terrorist laws over the London attacks to 20.
A major police operation was put into operation on the UK's transport system, with officers on a precautionary high alert to reassure the public and deter would-be attackers.
The funeral of Mr Menezes is to be held in his home town of Gonzaga on Friday.