RBS shares closed last week at 168.8p, down by roughly a third on the 502p that Gordon Brown paid to save the bank in the 2008 crisis.
It means that the taxpayer is sitting on a loss of £29bn, equivalent to a hit just over £1,000 for each of the UK's 27m households.
RBS was one of the institutions that saw trading in its shares suspended in the days after the Brexit vote.
The bank saw its stock plummet by around 20 per cent in the first day of trading after the referendum, and then on 27 June, it twice triggered London Stock Exchange circuit breakers, which automatically bring trading to a five minute halt if a stock falls by more than eight per cent from its opening price.
Last year, chancellor George Osborne sold a £2.1bn stake in RBS to cut the government’s holding from 78.3pc to 73.2pc of the bank.
However, further sales have long been in hold as the Treasury seeks to minimise the loss to the taxpayers.
Chief executive Ross McEwan last week described the Brexit vote as “a setback”, adding that it could delay the sale of the government's remaining holdings by as much as two years.
RBS will report first half results in early August.