Homeowners are being invited to share their internet connections with passers-by in return for the right to access the network via other people’s connections.

The attempt to expand the nation’s wi-fi network will mean that anybody with one of the latest mobile phone handsets, such as the Apple iPhone and some BlackBerrys, can access the internet through the front window of a participating home. People who sign up to the scheme, announced by BT and FON, a Spanish internet company, will be able to access the net through other people’s broadband connections and through BT’s 2,000 wi-fi hotspots. A typical home broadband router, which transmits the wireless signal, has a 30m range, making it easy for passers-by to “piggyback”.

Existing BT broadband subscribers will be able to join the scheme free of charge. Those with other providers need to pay a one-off £30 fee for a FON router, after which they can share their connection and access the internet whenever their phone is in one of the other residential hotspots.

There are now more than 10,000 wi-fi hotspots across Britain, the majority at airports, railway stations and cafés, but almost all are paid-for services, starting at about £6 an hour, or £10 for a day’s access. The thinking behind the new scheme is that, as more mobile phones are able to access the net via wi-fi, there will be demand for free internet access on such devices, so that popular services, such as music downloads, do not take so long. Accessing the web via a mobile phone network can be painfully slow.

Currently about 3 per cent of telephones in Europe have wi-fi capability but that figure is expected to grow to more than 40 per cent in the next three years, according to the analysis company Gartner.

FON would not say how many British residents were already signed up to its network, but it said that as soon as the number reached 50,000, the service would start to be useful.

Sceptics said that it was unlikely that people would be in the shared hotspots, predominantly residential streets, when they wanted to use free wi-fi, and that quality control would be difficult to maintain. Security experts also said that there could be significant risks for consumers in opening their home broadband connections. Paul Vlissidis, technical director of the security company NCC, said: “Wild horses would not get me to sign up to this. It is not just the risk of having personal details taken. What about if someone starts downloading child pornography via my connection? Am I implicated?”

Diego Cabezudo, FON’s chief operating officer, said that the public and private parts of the connection were kept completely separate and that visitors could not access documents stored on the homeowner’s computer.

Surfing on the move

— Wi-fi hotspots are pockets of “wireless connectivity” that allow any device with wi-fi capability to connect to the internet at broadband speed

— Most laptops and many high-end mobile phones, including Nokia’s N-series and some BlackBerrys, have wi-fi built in. According to Gartner, 40 per cent of phones will have wi-fi in three years

— There are more than 10,000 wi-fi hotspots in Britain, with the majority at transport hubs and hotels. McDonald’s, above, plans to have wi-fi access in all of its 1,200 outlets by the end of the year. The largest network is The Cloud, which supports more than 8,000 hotspots, including at most main airports, as well as Chelsea and Arsenal football clubs

— Wi-fi coverage is now offered in city centres, including Manchester, Edinburgh, Canary Wharf and the City of London

— In Silicon Valley, California, authorities are attempting to set up a large-scale wi-fi network that would provide internet access to 42 cities over an area of nearly 4,000 sq km (1,544 sq miles), but the project is struggling from lack of demand, as well as problems related to coverage

— Cybercriminals are now targeting wi-fi hotspots using “evil twin” attacks, where victims think they are logging on to a genuine network but are diverted to a rogue website, where their keystrokes are captured by the fraudsters