Barclays has been given a rough ride by shareholders as an apology by its chairman failed to quell anger over bumper pay awards.

At a packed annual general meeting in London, Marcus Agius was confronted with heckling, shouting and heated questions over the bank's remuneration, in particular the pay of chief executive Bob Diamond.

The American boss received £17.7 million in salary, bonus, benefits and vested long-term share awards last year, despite admitting his bank's performance was "unacceptable" in 2011.

While apologising for failing to engage with shareholders, Mr Agius said "the brutal reality" was that paying "zero bonus" was not an option.

Responding to a shareholder question about why Mr Diamond merited any bonus at all, Mr Agius said: "We operate in an international competitive industry. We have to fight for our business every day. It's not an option to pay zero bonus. We would be so far out of line with our competitors that the commercial consequences would be dire."

However, there was also anger among shareholders that the ratio of pay and bonuses to dividends was three to one. One said: "Barclays is not run for its shareholders, but as a milch cow for its officers and staff."

Barclays is expected to receive a bloody nose from shareholders when the outcome of votes at the AGM is released later. There was speculation in advance of Friday's meeting that as many as one third of shareholder votes will go against the reappointment of remuneration committee chairman Alison Carnwath and the 2011 pay report.

The Local Authority Pension Fund Forum, the Pensions & Investment Research Consultants and the Association of British Insurers warned members over the pay scheme. And institutional investors, including Fidelity, Aviva and Scottish Widows, said they would vote against the report or re-election of Ms Carnwath.

Defending pay, Ms Carnwath said: "We reduced awards significantly in 2011." In response, one shareholder heckled "not enough", triggering laughter and applause from the auditorium.

On Thursday, the bank reported an adjusted return of equity of 12.2% in the quarter - a key figure as Barclays has pledged to hit annual return of equity of 13%. Mr Diamond previously told shareholders it was "unacceptable" that the bank recorded a return of equity of just 5.8% in 2011, down from 7.2% the previous year.