Nomura, the Japanese bank, is set this week to table a £1.25bn bid for Associated British Ports, Britain's largest ports operator.
Guy Hands of Nomura, who is also bidding for Welsh utility Hyder, contacted the AB Ports board last week and has hired Warburg Dillon Read to advise. The port operator is expected to acknowledge the approach in a statement to the stock exchange on Tuesday.
An AB Ports source said the company had not sought offers and was taken by surprise by Nomura's interest. The company appointed a new chief executive, Bo Lerenius, last year to develop the business. It was recently forced to write off £80m because of a poorly performing American arm.
AB Ports shares closed at 264p on Friday, valuing the company at £875m. Nomura's strike comes at a time when the shares have been trading at five-year lows. The stock has fallen from 387.5p seen in 1998.
Nomura is believed to have been attracted by the strong and reliable revenue stream of the company. AB Ports was formed in 1983 by grouping together 19 ports.
The company now controls 23 ports spread across the country, including Southampton and Hull, and employs about 3,000 people. Its ports handle one-quarter of the UK's seaborne trade.
AB Ports also owns a container services business as well as thousands of acres of land around its ports, which it is developing.
AB Ports did not mention the approach from Nomura at its annual general meeting, which took place on Friday last week. Mr Lerenius simply told the shareholders that first-quarter trading was in line with expectations. The company's underlying profits rose by 3 per cent to £113.5m last year. Analysts forecast profits of £118m for the current year.
Nomura already owns an extensive pubs chain, the Thorn Television rental business and 57,000 Ministry of Defence homes.