ING said that it would pay a maximum of Bfr3,600 ( pounds 64) per BBL share and that it would partially finance the bid through a new issue of its own preference shares. The acquisition of all outstanding shares in Belgium's second-largest bank would require a maximum investment of 3.2bn guilders ( pounds 1.03bn).
ING, which currently holds a stake of about 10 per cent in BBL, said it would buy the 6.72 per cent of BBL shares held by two Italian companies as a first step towards the full public bid.
The Dutch group said it expected to make a final decision on the bid by mid-October and would reserve the right not to honour the bid if it failed to raise its stake in BBL to at least 51 per cent.
BBL, whose shares were suspended in Brussels at BFr3,275, said it would agree to ING's condition that ING receive full information about BBL's financial position.
ING will call an extraordinary shareholders' meeting on 12 October to authorise the issue of preference shares, which would carry a fixed 10-year dividend based on current market rates.
ING said the acquisition of BBL would enable it to realise its strategic goal of establishing a second home market in Europe.