Sir Nigel Rudd, the Williams chairman, is understood to have had informal contacts with Securicor and a formal bid for the manned guarding specialist could be tabled as early as this week.
One problem for Williams, which has long harboured ambitions of buying Securicor, could be the price. It is understood that it may need to pay at least pounds 1bn to ensure the recommendation of the Securicor board, which is led by chairman Sir Neil McFarlane, the former Conservative minister.
It could also face competition from Rentokil Initial, the services group run by Sir Clive Thompson.
Speculation of an imminent bid last week sent Securicor shares sharply higher in heavy trading. The move was triggered by the completion of the sale of Securicor's 40 per cent stake in BT Cellnet to British Telecom for pounds 3bn, a deal which has left Securicor especially vulnerable to a bid after it returned the proceeds to shareholders.
It is understood that several institutions, including Threadneedle Asset Management, have been buying Securicor shares ahead of next month's results, which are expected to be strong.
Williams has been keen for a deal since the breakdown of talks with Tyco, the American electronic components manufacturer. Sir Nigel is unhappy about Williams losing its place in the FT-SE 100 list of top British companies.
In recent years, Williams has been expanding its security systems and services division, which includes the provision of guards and close-circuit television systems.