Royal Bank of Scotland chief Ross McEwan will bow out with a final set of numbers on Thursday before handing over the reins to the lending giant's first female chief executive.

Mr McEwan leaves on October 31, paving the way for Alison Rose to make history as the first woman to run one of Britain's biggest high street banks.

However, the third quarter figures look set to be challenging for the outgoing boss after RBS warned it will need to take a hit of up to £900 million for payment protection insurance (PPI) after a last-minute surge in claims ahead of the August 29 deadline.

The part-nationalised bank, which is still 62% owned by the taxpayer, said the number of claims in August was "significantly higher than expected", with a spike in the final days before the cut off.

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It alerted over a charge of between £600 million and £900 million in its third quarter results, on top of the £5.3 billion it had already set aside to date for the mis-selling saga.

This looks set to dent its performance after a robust first half for the lender, which saw it deliver a £1.7 billion special dividend payout for shareholders, offering a surprise windfall for the taxpayer.

HeraldScotland:

Alison Rose and Ross McEwan

The divi cheer followed its highest half-year bottom-line profits in more than a decade, with attributable profits jumping 130% to £2 billion.

Meanwhile, operating pre-tax profits outstripped forecasts, rising 48% to £2.7 billion.

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RBS kicks off the third quarter earnings season for the major high street lenders, which is set to be dominated by PPI charges after a flurry of warnings after a pre-deadline claims frenzy.

Barclays, which reports on Friday, joined rivals in cautioning over a larger-than-expected PPI claims bill, saying it will set aside between £1.2 billion and £1.6 billion in additional cash for the scandal.

READ MORE: PPI claimants left waiting as banks swamped by complaints

The PPI debacle could cost banks as much as £53 billion, according to a forecast by think-tank New City Agenda.

The third quarter will also likely draw a welcome line in the sand on PPI for lenders.

Analysts are predicting total income of £3.5 billion, with an operating profit of £720 million.

Analysts at Jefferies said: "UK domestically focused banks are set to enter 2020 with PPI and Brexit, two areas that have impacted earnings, capital and suppressed valuation, behind them."