£3.9bn profits almost all due to US investment arm'Back to bonuses as usual', says Lib Dem spokesman

Barclays tonight said it was considering its "options" in the face of a government commission considering whether to break up the banks.

After it emerged that Barclays' investment banking arm had generated almost 90% of the bank's larger-than-expected £3.9bn first-half profits, its chief executive, John Varley, refused to give a clear answer when asked if the bank might move overseas if forced to break up by the commission.

The board is understood to have considered the issue and chairman Marcus Agius fuelled speculation about such a move today when he said: "I'm sure all banks are responsibly considering what their options might be."

The investment banking arm, Barclays Capital, amassed a £3bn pay and bonus pot for its 25,000 staff, and the Liberal Democrats used the division's contribution to the 44% rise in profits to call for banks to get "back to basic, low-risk banking".

BarCap's profits trebled to £3.4bn; the division making the next largest component of the profit was the UK high street bank which made £504m, a 61% rise. The improved profits were also boosted by a 32% fall in impairment charges to £3bn and included a number of accounting items. If these had been excluded, the profit figure would have been £3bn, up 22%.

In making a case for so-called "universal banks" like his, which combine high street operations with investment banking businesses, Varley pointed out that Barclays had made £25bn of profits over the course of the three-year financial crisis and had not needed taxpayers' money.

But Lib Dem treasury spokesman Lord Oakeshott said: "Barclays' bumper profits from their New York-based gambling operation, Barclays Capital, prove the urgent need to break up the banks. It's back to business and bonuses as usual as if the crash never happened. But businesses and homebuyers in Britain are still struggling for loans on sensible terms."

Barclays responded to criticism about lending by saying it lent £18bn to households and businesses in the first half of the year. The coalition government is considering lending targets, but Varley said: "It won't help those to whom we lend if we lend imprudently. One of the reasons [for the crisis] was that people were over-borrowing. Our owners expect us to lend prudently."

While other banks' shares rallied when they announced profits this week, Barclays' fell 4.5% to 324p as the City digested the importance of BarCap to the bank as a whole, and the fact it was showing signs of a slowdown.

Analysts were also concerned about increasing costs, which were up 21% at £9.7bn. Of the £1.6bn increase, some £1bn was down to BarCap, which employes 3,900 more people than a year ago.

The bank set aside 42% of the revenues generated by BarCap as pay – or 37% if gains on its own debt are excluded – while finance director Chris Lucas said the overall bonus pot for 150,000 staff was £1.7bn, including £400m of bonuses deferred from last year.

The bank set aside £194m to cover an investigation by the US justice department into violation of sanctions regulations and paid a second quarter dividend of 1p.