Efforts are being made to gather up to 20% of Securicor shareholders against the sale to BT. The deal had been agreed by the managements of both companies.

The proposal, announced in July, values BT Cellnet at about £7.88bn, or £2,730 per phone subscriber.

Some Securicor shareholders said they had expected more for the stake, particularly in the light of the £3,169 per subscriber which Deutsche Telekom agreed to pay earlier this month for another UK mobile phone firm, One2One.

"The One2One sale highlighted the low level that the Cellnet deal was struck at," a representative of Securicor's major shareholders, who did not wish to be named, was reported to have said.

Mercury Asset Management is Securicor's largest shareholder, followed by Standard Life Assurance, Threadneedle Investment Management, and Morgan Grenfell Asset Management.

Cash for upgrade

Other shareholders include Perpetual Investment Management and several US fund managers based on the East Coast.

Some of the fund managers say that if a higher price can not be negotiated, they may vote against the sale on 14 October, when the company holds an extraordinary general meeting.

When the sale was announced in July Securicor said it had investor support, even though most market analysts said BT would get the outstanding stake cheaply.

BT was seen as the only buyer for the stake, while Securicor was faced with injecting a substantial amount of cash to upgrade the network.

Apart from its equity stake in BT Cellnet, Securicor's only participation in the management of the company was the three seats it held on the seven-seat board.