The UK’s biggest banks are set to slash the value of their balance sheets as analysts complain of a lack of clarity in accounting for sub-prime related issues.

The major banks release their final figures next week, with the figures likely to draw an unprecedented level of scrutiny following the implosion in the US sub-prime market.

Analysts said they were still in the dark about the likely impact of the US problems, and added that the disclosures themselves might only be a partial guide.

‘The disclosures are horrible and completely unhelpful,’ said Mamoun Tazi of MF Global Securities, referring to off-balance sheet disclosures in particular.

The banks face scrutiny of two issues in particular: both the structured investment vehicles they partly sponsor which invested in sub-prime assets, and the assets they hold on balance sheet which are likely to be written down.

‘We can’t get a sense of the worth of the assets and the company’s liabilities because we can’t get a view of the exposures that relate to them,’ said Tazi.

Barclays, Lloyds TSB, Standard Chartered and RBS are all set to publish their preliminary numbers in the next fortnight. Auditors will then further pore through the figures to deliver their verdict.

Several analysts said that they expected further huge writedowns, but the City has found itself blinkered about the level of exposure.

‘The visibility to make that kind of judgment is missing,’ said Tazi.

‘We don’t have enough disclosures of that type to come up with anything specific,’ he added.