Virgin Media has been awarded the contract to provide Wi-Fi access on London Underground platforms, with mobile internet services set to be available in time for the London Olympics.

The service will initially be rolled out to 80 stations by July, and 120 by the end of the year, following a competitive tender run by Transport for London.

The Wi-Fi connections will only work at station platforms, though – not while trains are travelling through the tunnels.

"Millions of passengers will now be able to connect to their work, friends or access the latest news and travel information whilst on the move," said London mayor Boris Johnson.

"This is a fabulous new and free resource which will be in place from this summer when London is being showcased on a global stage and playing host to millions."

The service, which will give access to mobile internet via a TfL portal offering travel, news and entertainment bulletins, will remain free for Virgin Media customers after the Olympic Games.

Other users will only be able to access a limited amount of free content on the TfL portal, with full mobile internet services offered on a pay-as-you-go basis.

Virgin Media is building the Wi-Fi network from a total capital expenditure budget of about £640m for 2012, set at between 15% and 17% of the cable company's £4bn in revenues.

"With the eyes of the world on London this summer, we'll be showing off our capital as a leading connected city on the global stage," said Neil Berkett, chief executive of Virgin Media.