Royal Bank of Scotland shareholders who make the journey to its Gogarburn headquarters for the annual meeting will today have their first chance to quiz new chief executive Ross McEwan.

It comes as the interest rate swap mis-selling saga continues to dog the banks, with a reported claim from a City derivatives expert that RBS and Lloyds face legal claims from bigger customers of £5 billion each, dwarfing their combined £1.5 billion provision for redress to smaller firms.

Over 10,000 supposedly "sophisticated" borrowers were excluded from the bank-led mis-selling review, on size-related definitions, forcing a significant number of firms to go to law.

Specialist adviser Lexlaw commented: "There is no doubt that the bank are facing claims which far outweigh the figures they are disclosing via their accounting procedures."

Vedanta Hedging said: "There are hundreds of cases that are settling and have settled over the last two years."

The Herald reported last week that banks are adopting a robust approach to businesses' claims for consequential losses.

Nasar Zamir, principal at Congruent Financial Partners said he stood behind his estimate of £4.5bn — almost 10 times the bank's current £530m provision — for new liabilities at Lloyds. A Lloyds spokesman said the calculations were "highly speculative, based on assumptions that are just not credible and we refute them completely".

Mr McEwan meanwhile will want to remind shareholders of the bank's £1.2 billion first quarter statutory profit, the best since the crash, the two-thirds drop in bad debts, and the promise of no further mis-selling provisions.

The new chief executive may suggest that the anticipated rise in interest rates will help the bank's margins, and that the sale of US subsidiary Citizens is under way.

He may be questioned on reports that a private equity deal to resuscitate Ulster Bank could add 30p to the bank's share price, and on the EU pay cap on bonuses, which RBS wants to circumvent with share awards.

The RBS board may be asked to update shareholders on the four separate court actions against the bank, involving major financial institutions including Standard Life, which allege shareholders were badly misled over the bank's 2008 rights issue.

Estimates of the total claims range from £4bn to £7bn, and Mr McEwan has already claimed that RBS will not be forced to early settlement but wants to tough it out in court.