There are many tools on the web that allow investors to track the value of their portfolios. British taxpayers, now major holders of RBS and Lloyds Banking Group, can turn to two unlikely sources to follow the value of their investments in the beleaguered banks: the websites of the treasury and the National Audit Office.

Yesterday, the treasury published details about the £282bn (US$459bn) in assets it will guarantee from RBS. The bank is on the hook for the first £60bn in losses on the portfolio, with the government footing the bill for any additional write-downs. The treasury says it does not expect losses to exceed £60bn, but anyone willing to trawl through the 20-odd pages of asset inventory can judge for themselves (£34bn in CDSs and CDOs with a “particular high-risk profile” doesn’t sound very promising). And in what has become a common theme, Britain’s asset guarantee covers a large share of loans taken out by foreign borrowers, a politically unappealing outcome.

Asset guarantees comprise only part of the bank bailout. Direct equity injections of nearly £70bn for RBS and Lloyds should make taxpayers particularly interested in the fate of these banks’ shares. Last week, the National Audit Office, a government spending watchdog, published a report that included calculations of the break-even price for the government’s holdings in RBS (50p) and Lloyds (74p). Every 10p rise in the banks’ share prices from these levels adds £9bn to the value of the people’s stake in RBS and £3bn in Lloyds. When the report was written, in late November, the holdings were worth £18bn less than their purchase value. Shares have fallen further since. Maybe it’s best not to check up on the value of this portfolio too often.