City watchdogs were monitoring cash withdrawals from Royal Bank of Scotland every hour during the height of the banking crisis, the Guardian can reveal.

The Financial Services Authority demanded 60-minute updates on cash flooding out of the bank's branches and hole-in-the-wall machines in the days before Britain's historic bank bailout, which took place a year ago.

The regulators stepped up their surveillance after realising that confidence was draining from the banking system following the collapse of Lehman Brothers a month earlier, and that customers were concerned about the safety of their deposits.

The chancellor, Alistair Darling, sanctioned the government's taking a 70% stake in RBS, and 43% in the combined Lloyds and HBOS, after a series of frantic round-the-clock meetings that weekend. A year on, those shareholdings are creating a £4bn paper loss for the government.

The taxpayer breaks even when Lloyds shares rise through 122.6p and those in RBS trade above 50.5p. On Friday, the banks' shares closed at 94p and 48.34p respectively.

The Guardian has learnt that a year ago the City regulator was so concerned about customers' fears over the soundness of RBS that withdrawals on the high street were being scrutinised hourly, as well as the activities of big business and rival banks, which were also losing confidence in the troubled bank.

The pattern of withdrawals is crucial, as banks rely on customers on the high street and in the money markets for deposits which, in turn, secure the loans and other businesses operated by banks.

While there were no queues around branches in the way there were when Northern Rock ran into difficulties two years ago, the dramatic pace of withdrawals left the authorities with little option but to bail out the weakest high street banks to avert their collapse.

The regulator knew how fragile the system was after embarking on emergency surveillance of the high street banks to understand the extent of the outflows facing the weakest players.

Hector Sants, chief executive of the FSA, has already admitted that the regulators could not have allowed RBS and HBOS to open for business on Monday morning a year ago unless a solution had been found to pump more capital into them.

Despite sitting on a loss on the current investments in Lloyds and RBS, the taxpayer may yet be prevailed on to put more cash into Lloyds if the bank decides to proceed with multibillion-pound stockmarket fundraising to reduce its reliance on the asset protection scheme, the government's insurance for toxic loans.

The asset protection scheme was announced in January to insure £585bn of bad loans at Lloyds and RBS, though the improvement in market conditions since then has prompted both banks to rethink the terms they are prepared to pay for the insurance.

Lloyds is believed to be most determined to reduce the £260bn of loans it has agreed to insure, but that means it needs to raise up to £25bn – equivalent to its current stockmarket value. A cash call might help find some of the money required, and, if Lloyds were to embark on a rights issue, it would mean that the taxpayer would have the opportunity to match its 43% stake in the bank. This would require UK Financial Investments, the body which controls the taxpayer stakes in the bailed-out bank, to ask the chancellor for more funds for the bank.

Lloyds has paid back about £2bn to the Treasury after a placing in June to convert preference shares issued to the government into ordinary shares.

In other countries where banks received capital injections from their governments, money has been paid back faster. The Swiss government made a Sfr1.2bn (£734m) gain when it sold its 9% stake in UBS in August. In France, the banks that were bailed out have also taken steps to repay their government's investment.

Both Société Générale and BNP Paribas are conducting cash calls to pay back state support, while the chief of staff at the Elysée has said that the French banks will soon have paid back all their loans, and that the French state would have received €500m (£464m) as a result.

It is reported today that Barclays is planning to sell off £4bn of its assets, in a bid to allay shareholders' fears over its investments and the ongoing risks posed by toxic assets. The Financial Times says that the bank is looking at a deal to shift up to £4bn of the assets off its balance sheet, in an echo of a similar transaction it undertook last month with a £12.3bn portfolio.

• This article was amended on 12 October 2009. The original converted Sfr1.2bn as £7.3bn. This has been corrected.