The company has also asked its broker, SG Warburg, to investigate the reasons behind a rapid rise in the company's share price 10 days ago. The Stock Exchange is also investigating the price movement.
It has also emerged that some of United Biscuits' directors would stand to receive more than £1m each if control of the company changed hands. The directors have additionally benefited by changes to the company's long-term incentive scheme. New rules make it easier for the directors to make big cash gains.
United Biscuits has sent out notices under section 212 of the Companies Act, which force nominees listed on the company's share register to divulge the beneficial owner of the stake. The company recently stepped up its surveillance of nominee accounts to flush out holdings in excess of 70,000 shares.
John Warren, finance director, said: "Every time we pick up a paper United Biscuits is down as a likely candidate for takeover. Given that situation, it is likely United Biscuits' management are keeping a close eye on the share register."
The Stock Exchange is investigating a 23p jump in the share price a week last Friday. It fell 19p on the following Monday. Market sources believe the rise was caused by a maverick broker talking up bid rumours to make a quick profit.
In the event of a takeover, United Biscuits' executive directors, who are all on three-year rolling contracts, could be in line for pay-outs that in some cases would top £1m.
Eric Nicoli, the chief executive, on a base salary for 1994 of £386,250, could expect more than £1.15m to buy his contract out. Brian Chadburn, the head of the company's US operation, who is paid $556,400, could take away $1.67m (£1.1m).
Under changes to the company's incentive scheme for senior managers, there are bonuses if United Biscuits' earnings per share show real growth of 3 per cent. Instead of the cash payments made under the earlier scheme, the directors are to receive shares. Mr Nicoli's share bonus this year could be worth up to £715,000.