BT is to step up its fightback against Britain’s mobile operators by significantly extending its wireless broadband service.

The telecoms giant, which wants to offset the slowdown in its traditional calls business through “new wave” services such as broadband, will today unveil plans to boost wi-fi coverage for its 3.7 million retail broadband customers. They can access the wireless service mainly through BT Open-zone “hotspots” and those operated by The Cloud, the 3i-backed wi-fi firm.

Analysts believe that the announcement will include a new partnership or an extension of BT’s tie-up with The Cloud.

Wi-fi gives consumers broadband on their laptops at home, or on the move, without a cable. Mobile phone handsets are also being produced with wi-fi chips that will enable users to bypass their 3G mobile network and make cheap calls over the internet. The technology has alarmed many mobile operators, regarding it as a threat to their revenues.

After demerging its O2 mobile operation, BT does not have a mobile network of its own – a factor regarded as a key weak spot by many analysts. Alhough it runs a service over Vodafone’s network, it has just 304,000 mobile connections – down from 372,00 in 2004.

Technology such as wi-fi and wi-max – wi-fi’s more advanced rival that works over a broader area and at faster speeds – could help BT to overcome that problem, analysts believe.

Initally, wi-fi services were mainly available in busy locations such as coffee shops and airports. Providers include T-Mobile and The Cloud. However, entire areas are now being covered.

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