Firms in the UK are desperately keen on boasting about their US counterparts – until they hit trouble, that is.

KPMG's tax issues in the US were one thing. BDO's problems with its US firm BDO Seidman look equally troubling.

A jury has ordered the firm to pick up a $350m (£176m) bill for not picking up a fraud at Bancest. That is on top of a $170m damages in another lawsuit on the issue.

The $520m bill is close to Seidman's $550m turnover for 2006. 'It's an astronomical verdict based on the size of the firm,' said US accounting analyst Art Bowman.

Such cases, of course, rarely actually mortally damage firms. With KPMG, it appealed to the US Justice Department to avoid a prosecution. Pleas that a firm will be destroyed by a verdict or regulatory move are often the trump card in such disputes. With concentration of the market at the top end on everyone's minds, that's understandable.

Seidman has been robust in its defence, saying: 'BDO Seidman respectfully but forcefully disagrees with this verdict. The firm intends to ask the trial court to set it aside and, failing that, to appeal. This is an interim decision in a long process and a contingency that was anticipated. We remain confident of achieving a just resolution at the appellate level.'

Such a move seems likely. A key part of the damages claim relied on a finding of 'gross negligence'.

'We believe that interim finding was the product of the jury not being permitted to hear major portions of our defence during that part of the trial. We therefore believe the gross negligence finding and punitive damages will not survive the appeal in this case,' says Seidman.

The alternative could be extremely worrying for BDO Stoy Hayward in the UK, which relies on Seidman for its exposure to the US. Its clients with US operations need Seidman's assistance there, and it will get referrals from there too.

There are a couple of things to note too. Seidman has a habit of taking cases on, and winning. Admirably, perhaps, it does not just pay out.

The International network has also beaten off an effort to make it jointly liable for the claim.

Stoy Hayward is understood to be relaxed about the claim, but there may be a few sleepless nights yet.