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Mobile network O2 has become the latest to offer its customers access to free wi-fi on London's Tube platforms.

It joins EE, Vodafone and Virgin Media in offering internet access on the Underground, leaving Three customers as the only mobe users who can't connect while commuting.

However, Virgin hasn't managed to conquer the abrupt and very annoying connection dropout which occurs whenever trains enter a tunnel.

Virgin Media offered Wi-Fi connections to some 700,000 people during the Olympics, but announced in November last year that customers who weren't on the right network - namely its own, EE or Vodafone - could pay £2 a day to access the internet while underground.

Mark Williamson, Head of London Wi-Fi at Virgin Media, said: "Wi-Fi on London Underground has gone from strength to strength and we're delighted the majority of Londoners are staying connected for no extra cost.

"Virgin Media's unique fibre optic network means we deliver unrivalled capacity for next generation digital services both inside and outside the home, meeting the increasing demand for wireless services."

Virgin Media has also announced plans to bring wireless to 12 more Tube stations around London: Acton Town, Baker Street, Bank, Caledonian Road, Earl's Court, Holland Park, Ladbroke Grove, Maida Vale, Queen's Park, Shepherd's Bush, Sloane Square and West Ruislip.

The main problem with providing full Wi-Fi connectivity in London's tube tunnels is the lack of available space. With a train-roof-to-tunnel clearance of just three inches on the deep level lines and essential signalling kit taking up most of the remaining room, the logistics of piping cat photos onto underground mobes has so far eluded network engineers.

More than 100 stations now have wireless internet connections. To get a free ride, connect to "Virgin Media wi-fi" at a station and enter your account details. ®

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