Westpac Banking Corp is expected to outline details this morning of a $19 billion friendly takeover of St George Bank in a move that would create the country's biggest bank by market capitalisation and might force a rethink of the four pillars policy that restricts takeovers between the Big Four banks.

The planned takeover of the former building society is likely to face competition-related hurdles given that it would deliver Westpac a dominant slice of the NSW and South Australian home and business lending markets and make it a powerful force in funds management.