That well exceeds feasible cost synergies of 40% in the UK based on past transactions, analysts at BofA said in a report. The bank said the deal will generate a return on invested capital of over 20% and help lift the UK business' return on equity to 16% from an industry-lagging 11%. Integrating computer systems and migrating customer accounts has proven a tough task in Britain due to a reliance by lenders on often decades-old legacy software. Two of the sources close to the process said Santander would use Gravity, its new IT system, to help with the integration. The Spanish lender's aim to cut costs by slashing branches and jobs may also trigger protests from unions and customers, as well as political scrutiny. Santander will also have to battle to win market share from Lloyds Banking Group (LON: LLOY ) and NatWest that dominate more profitable banking services such as mortgages and credit cards, even with the scale it has added by buying TSB. ($1 = 0.7346 pounds) ($1 = 0.8480 euros)