Royal Bank of Scotland nearly doubled pre-tax profits to £2.65 billion in the first half of the year, despite taking an extra £250 million hit for mis-selling financial products.
The state-backed lender published interim results a week early, saying it was because they were "significantly stronger" than market expectations.
Pre-tax profits for the first six months of 2014 were up from £1.37 billion the year before, RBS said.
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But for the second quarter they were 38% lower at £1.01 billion as the group took a hit from restructuring costs and provision for compensation for the mis-selling of payment protection insurance (PPI) and interest rate swaps.
Chief executive Ross McEwan said the results showed the underlying strength of the business, but warned there remained "bumps in the road ahead" as it continued to deal with scandals of the past and dispose of toxic assets.