The last sanctuary from the incessant red light blinking on BlackBerry devices will begin to vanish in the next few weeks as Wi-Fi coverage is extended to the London Underground.

Passengers will be able to check emails, browse the internet and even attempt to watch live TV on their mobiles, tablets and laptops while waiting for trains at 80 stations across the network. Another 40 will be connected by the end of the year.

The service, which will be free to everyone for the whole summer, is expected to come online at some stations, including King's Cross, Leicester Square, Oxford Circus and Stratford, within the next couple of weeks.

Virgin Media, which is providing the service in partnership with Transport for London (TfL), said passengers would be able to connect to the internet in ticket halls, on escalators and platforms and from inside trains waiting in stations.

Coverage will be lost when trains enter tunnels, but Virgin said customers would be automatically reconnected upon arrival at the next station.

"Your pages will update as soon as you enter a new station, so you will be able to tweet your journey," a Virgin spokeswoman said.

The first tweet from the underground was posted by Rory Cellan-Jones, the BBC's technology correspondent, who managed to stream an episode of The Apprentice on the BBC's iPlayer on his iPad.

Ordinary users, however, will struggle to get speeds anywhere near fast enough to stream video as the service is likely to be overloaded by the number of passengers trying to connect.

Virgin said speeds would be "comparable" to the planned 4G mobile phone internet.

The service will only be free for everyone until the end of the London 2012 Olympic Games. Customers of some Virgin broadband packages will continue to receive free access; pay-as-you-go access will be available to others.

The Virgin spokeswoman said she hoped passengers would be considerate to others and refrain from accessing inappropriate or noisy sites.

The Wi-Fi move follows several unsuccessful attempts to bring mobile phone coverage to the London Undergound. The latest attempt fell through last year even though the state-owned Chinese company Huawei offered to provide £50m worth of technology as a gift between Olympic nations.

Mobile coverage is already available on several underground networks, including Glasgow's Subway, but TfL claimed London would be the first deep-level network to be connected.

Passengers travelling to the Olympics through the Channel tunnel will also be able to use their mobiles despite being 75 metres under the seabed after French operators extended mobile coverage along the entire 23-mile link.

Mobiles will not work on the return journey, however, because British mobile operators, who hold the rights to the Folkestone-Calais tunnel, failed to agree on how to finance the project.