The successful bidder for EBS Building Society will be expected to consolidate assets from Anglo Irish Bank, Irish Nationwide Building Society and possibly other orphaned financial institutions as an implicit condition of the sale, according to informed sources.

The requirement will add hundreds of millions – possibly billions – to the bill for acquiring the nationalised mortgage lender, ensuring a deep, long-term commitment to the Irish market.

Banking sources said the government, acting through the National Treasury Management Agency (NTMA) and with the help of outside consultants, is intent on reshaping the post-transaction banking landscape and protecting against asset stripping if a private equity buyer wins the bid.

The government is expected to reveal its two-bidder shortlist tomorrow. It is understood the finalists are Irish Life & Permanent and a consortium of private equity investors, including billionaire Wilbur Ross and the Carlyle Group, fronted by Dublin-based Cardinal Asset Management. Private equity contenders Doughty Hanson and JC Flowers are believed to have fallen out of the running.

It is understood the Department of Finance wants any buyer to mop up some of the remains in the market from Anglo and Irish Nationwide, which together will have about €12.5bn in good assets post-Nama. Bank of Ireland's building society, ICS, which the European Commission has ordered the bank to sell, could also be in play.

IL&P is expected to merge EBS with its banking arm, Permanent TSB, to expand its footprint in the savings and home loans markets, a move on the cards since former IL&P chief Denis Casey started talks with EBS chief executive Fergus Murphy in 2008. Some sources have said a tie-up between the two mortgage lenders could lead to heavy job losses, an outcome they said the government is keen to avoid.

The Cardinal consortium is also thought to be interested in buying other institutions in the market, which could advance the government's consolidation agenda. Sources said all the bidders understood that market forces were driving a need for mergers among the smaller players in Irish banking.

Whoever is selected to buy EBS will have to fill its large capital hole. The government has already put in €100m in cash and €350m in promissory notes to recapitalise the mutual after it took huge writedowns on property development loans, but it will need €775m more to meet minimum capital requirements.

IL&P reportedly has been courting underwriters, including Citigroup and Deutsche Bank, for a €925m fundraising in the event it wins the bid.