The statement fuel the debate merger accounting and efforts by the International Accounting Standards Board to abolish merger accounting.
Speaking at the IoD conference at the Royal Albert Hall, Mathewson insisted NatWest had been fully integrated into RBS because of the way it had been acquired.
He said: ‘We could not have done this if the acquisition had been a merger, we could only have done it as a hostile takeover.’
Within three days, he added, NatWest head office had been closed and they had chosen the best employees to remain with RBS.