T-Mobile and 3, Britain’s fourth and fifth-biggest mobile phone operators, will today unveil a plan to cut costs by pooling their networks.

The alliance between the two previously bitter rivals will fuel speculation that the companies might eventually merge.

The UK, with five network operators, but none with more than a 30 per cent share of subscribers, is one of Europe’s most fiercely competitive mobile phone markets.

The operators are each seeking to gain a market advantage through aggressive pricing, while cutting costs to claw back some of the billions of pounds they spent on acquiring their 3G licences.

At present, 3, which is owned by Hutchison Whampoa, the Hong Kong conglomerate, covers about 90 per cent of the UK population with its network. T-Mobile covers about 84 per cent.

Sharing 3G networks should enable the pair to slash the bill for rolling out infrastructure across the uncovered parts of the country. It could also allow the two companies to decommission some existing towers. The alliance could also trigger job losses.

T-Mobile and 3 are expected to insist today that their alliance will go no further than the plan to pool networks.

Vodafone and Orange have already announced a plan to share their networks in a deal that is expected to provide annual savings of up to 30 per cent. But it is thought that the T-Mobile and 3 negotiations are more advanced.

Bigger rivals, including O2, have long predicted consolidation in the UK’s mobile market and 3, as the weakest player, looks the most vulnerable target.

Last year, advisers for the group sounded out potential buyers. 3’s Italian operation is also known to have been touted around after a failed flotation attempt.

Speculation about 3 UK was fuelled late last year when Arun Sarin, the head of Vodafone, said that he would look at 3’s European assets if they went up for sale.

But Canning Fok, a director of Hutchison Whampoa, said that he would drive a hard bargain and urged Mr Sarin to put his money where his mouth was. He said: “I do not know whether he [Arun Sarin] has the money. I do not know how much money he has. If someone wants to buy . . . he has to have enough money.”

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