Transport for London has issued a warning over spam emails containing fake safety advice.
The emails claim to provide an emergency number that can be used underground and relayed via satellite. There are no mobile phone transmitters on the London Underground and satellite signals cannot penetrate below ground.
The email body reads: "If you travel to work on the tube please note the following information: if your mobile phone has no signal (so even if you were in a tunnel) if you dial 112 it diverts to a satellite signal and puts you through to the 999 call centre.
"All phone companies have signed up and as it is a satellite service it also gives them a trace to you if you don't know where you are."
The email may originate in Europe, since 112 is the European version of the UK's 999 emergency number.
A Transport for London spokesman said: "This email is incorrect. The 112 number does link people through to 999, but it only works if you have a signal on your mobile phone. If you have no signal bars on your phone, it will not work."
Mobile phone coverage for the Underground is planned for 2008.
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