Some of the threats by British companies to quit Britain for more tax-friendly shores is sabre-rattling. Companies can scent a weakened government desperate for the beating up at the polls and in the media to stop and are opportunistically piling on the pressure for tax concessions. (Yesterday's decision to allow pub companies to put their properties into tax-shielding real estate investment trusts will only strengthen the view that ministers are willing to yield.)

Some of the threats are hollow. Some of those complaining most vociferously pay no UK corporation tax at all and are merely pressing to head off reforms that might start to cost them in future. Fiscally at least, their exodus would be no great loss to Britain.

But for some genuine taxpaying companies, a tipping point has been reached. According to one of the big accounting firms, corporate clients are queueing up to revisit the whole question of tax domicile. For them the pros are starting to outweigh the cons. They are prepared to go through the cost and inconvenience of moving top people to, say, Dublin for the prize of having overseas profits taxed at 12.5 per cent rather than 28 per cent.

And it does mean inconvenience. The tax authorities here are not going to sit by and allow companies to duck tax simply by fixing a brass plate to a Georgian town house on St Stephen's Green and carrying on as before. They will regard that as a sham. There are other drawbacks too. Emigrating companies can expect less help from ministers when it comes to lobbying in Brussels or Washington and a less favourable reception when pitching for government contracts.

So far no major blue chip has made the move. But it would only take one household name - an HSBC or Glaxo - for the simmering discontent to erupt into a major row, one that would dwarf the stoush over non-doms.

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