Regus, the office supplies company, followed engineering firm Charter and the asset manager Henderson Group by announcing it was moving abroad to avoid uncertainty over Britain's tax regime.

Concerns were triggered early in the summer when the treasury announced it was looking at new plans for taxing profits earned overseas. Pharmaceuticals firm Shire and the publishing group UBS were the first to say they would move offshore, followed by several others including advertising giant WPP. Aberdeen Asset Management said it was monitoring developments and Scotland on Sunday revealed that three or four clients of Scottish-based Deloitte were also watching with interest.

Despite a partial climbdown by the Treasury, which agreed to review the proposal, Darling kept the door open for further changes. That was enough to force the hand of some firms. Regus will relocate to Luxembourg, while Charter and Henderson are off to Ireland.

The Government called in CBI director-general Richard Lambert to help it firm up a plan and it will be interesting to hear if he has anything to say on the subject when he addresses the CBI Scotland dinner in Glasgow this week.

Lambert is also engaged in the debate over a proposed windfall tax on energy companies. With several explorers and oil services companies enjoying record profits they are seen as easy prey for those who see them as there for the Treasury's taking. For the Chancellor, there could be no simpler way of raising badly needed cash to hand back to those struggling to make ends meet.

There is a growing clamour to raid the oil companies' bank accounts and those of the electricity and gas firms. Two more, npower and ScottishPower, raised prices last week, contributing to the biggest price rises in energy bills since the market was privatised.

The issue of fuel poverty – when 10% of household income is spent on energy – has risen up the political agenda and it is difficult to see how the Chancellor can avoid the calls to do something to alleviate hardship, not only among core Labour supporters, but the middle classes who will be more willing to desert the party.

Yet the introduction of a windfall tax, while easy to implement, is more difficult to justify. Bill Transier, chief executive of North Sea explorer Endeavour International, told this newspaper in June that the Government risked undermining one of its greatest assets if it imposed such a tax.

It would disincentivise companies from investing and therefore reduce tax income, and in comments made yesterday Lambert said that a retrospective windfall tax levied after the event would undermine investment decisions made in good faith. At least the windfall tax imposed by Labour on the utilities when it came to power in 1997 was included in its manifesto.

If the tax doesn't deter companies from investing, it would force them to pass the cost on to customers and suppliers so the benefits of a windfall would be lost elsewhere in the economy.

With energy companies already among the biggest contributors to the Exchequer, Darling may be playing with fire if he should attempt to squeeze even more from companies that need to make big profits to meet the rising cost of investment required over the coming years in hostile and difficult environments.

Gordon Brown has also called for them to increase supplies to help ease the oil price.

Add to that their requirement to meet renewables targets and the soaring price of energy on the wholesale markets and anything that discourages investment appears foolhardy.

It proves to be a difficult balancing act for Alistair Darling as he grapples with the twin challenge of companies escaping Britain's already tough tax regime and energy companies resisting even higher taxes.

Forth Ports braced for stormy ride

Our revelations last week of investor unrest at Forth Ports prompted chief executive Charles Hammond to reject calls for a break-up. He told the Financial Times on Friday the two sides of the business give value to each other. But the company has deferred spending on its property portfolio and that will test the patience of some shareholders.