Plans to allow mobile phones to work on London's Tube should be scrapped in case they are used in a terror attack on passengers, says Simon Hughes.
Mr Hughes is to unveil a series of anti-terrorist measures
The Liberal Democrats' London mayoral candidate said mobiles were a "cheap and effective long-range detonator".
Reassessing plans to allow mobiles to work on the Tube is part of Mr Hughes' new 10-point terrorism initiative.
He said: "Using mobiles on the deep line sections... is unnecessary. Texting is a luxury, security is not."
London Underground (LU) has been in negotiation with the four main mobile phone companies with a view to establishing subterranean transmitters in stations and even in tunnels so conversations could continue deep underground.
But Mr Hughes said the "precautionary step" of banning the use of mobiles was one way of helping prevent a Madrid-style terror attack on a soft target.
"By taking little precautionary steps and maintaining the public's vigilance London can help itself to stop an attack," he said.
Other measures in Mr Hughes' proposals include a new MI5-trained anti-terrorism adviser.
He will unveil his plan during a trip to Canary Wharf, scene of an IRA attack in February 1996.
Mr Hughes is due to be joined by Lib Dem leader Charles Kennedy.
He will say: "The war in Iraq increased the risk of terrorism in London even more than before.
The threat of terrorism has not, and will not, go away. Warnings from the Met Police show that we cannot afford to be complacent.
Mr Hughes is the Lib Dem candidate for London mayor
"The Met Police have done a magnificent job so far in preventing an attack on London, but it is vital that sensible, simple measures are taken to stay one step ahead of any terrorist plans."
"My proposals aim to both prevent a terrorist attack by encouraging more vigilance, and better protect people if there is an attack."
Mr Kennedy is due to back Mr Hughes' 10-point plan as a "necessary and sensible precaution" against terror attacks.
Mr Hughes' proposals:
Appointing a new MI5 trained anti-terrorism
specialist to advise the mayor of London.
Met Police training for businesses and their fire marshals setting out what they should do in the event of an attack
Setting up a dedicated London Emergency Volunteer Reserve Force to assist the emergency services in case of an attack
An annual anti terrorism summit with mayors of other global cities and their police chiefs to share best practice
The merging of British Transport Police in London with the Met Police
A reassessment of talks on installing mobile phone access on the deep line Tube network
Council tax bills to contain information on what to do in the event of an attack
Expand schemes to encourage train and tube staff to become special constables in the newly merged Transport division of the Met Police
Staffed police boxes at every mainline station during rush hour
Promotion of community events across London by the mayor to improve cohesion and understanding between different faiths and cultures to reduce suspicion and fear