As Gordon Brown moved on Wednesday to allay City concerns by promising cuts to corporation tax, a survey by the Financial Times revealed a level of dissatisfaction with his tax regime among some of the UK’s biggest companies.

It emerged that International Power is considering moving its corporate headquarters away from the UK because of looming tax reforms. In addition, two more of the companies surveyed, Aegis and ITV, said they were also watching developments.

Their comments follow hints that AstraZeneca, GlaxoSmithKline and WPP are also contemplating moving their tax domicile. Concern about companies migrating to lower-taxed jurisdictions has come to a head after recent announcements by Shire, the pharmaceutical company, and UBM, the business media group, that they are switching their tax domiciles to Ireland. The Treasury’s proposed reforms of the way it taxes companies’ foreign profits have fanned the flames.

International Power, which owns power stations in 20 countries and makes most of its profits outside the UK, is based in London. But it is looking at relocating to countries including Ireland and Switzerland in order to pay less tax.

The company said: “A significant proportion of our earnings are derived from outside the UK and therefore, like many UK multinational companies, we are considering the most appropriate financing and tax structure for the business, but we have not made any decisions at this stage.”

Of the 79 FTSE 100 companies surveyed by the FT, 54 either said they had no plans to relocate their headquarters from the UK, or explicitly ruled out such a move. A further 10 privately said they were not contemplating a switch.

Many – particularly those with “British” in their name – were emphatic. British Airways, the flagcarrier, said: “We are staying put.” BP said: “We would not do that.” Unsurprisingly, the London Stock Exchange said that it had no plans to leave the UK.

Others, however, were more ambivalent. Two companies would not be drawn on whether they had plans to move their domicile: Diageo, the drinks group, which owns Dublin-based Guinness, and Man Group, the world’s biggest listed hedge fund manager.

There is no suggestion that these companies are mulling a defection from the UK. But their reticence serves to remind policymakers of vulnerable sectors.

AstraZeneca refused earlier this week to rule out relocating its headquarters for tax purposes.

The Anglo-Swedish pharmaceutical group said it was “engaged in ongoing constructive dialogue” with the government on taxation of foreign profits.

Simon Lowth, finance director, said: “The board is obliged to consider all potential enhancements to shareholder value, corporate structure group domicile being one element...but as yet we don’t have any formal plans to change the existing structure.”

In a further indication of particular anxiety about the proposed changes in the pharmaceutical sector – whose overseas intellectual property might face greater scrutiny from Revenue & Customs under the plans – GSK joined the chorus.

“We have no plans at present to relocate our headquarters for tax reasons,” the company said. “However, we believe that the UK business environment has to be realistic so it doesn’t impair our ability to compete globally, and it is important that the government ensures that the UK is an attractive location for companies who have headquarters here.”

Other sectors with significant amounts of intellectual property that could be affected by the changes include media and consumer-product companies.

ITV – among the companies that have not categorically rejected such a move – said: “We have very different geographic revenue and profit derivation than UBM and we will watch the position as it develops.”

Robert Lerwill, chief executive of Aegis, the advertising group, added: “If there are ways to get better shareholder value through change of domicile, [companies] will have to look at it.” WPP, Sir Martin Sorrell’s advertising group, warned this week it might relocate its domicile, depending on how the Treasury’s plans evolved.

Six of the FTSE 100 companies, such as Royal Dutch Shell, Experian and Antofagasta, already have all or part of their headquarters abroad for operational reasons. Xstrata, the miner, is domiciled in Zug, Switzerland, for tax purposes.

One company said privately it was “keeping its powder dry”, while another said it had considered a move in the past and kept its tax domicile under review.

Highlighting another area of concern for the City, Lord Levene, chairman of Lloyd’s of London, said simple changes to the timing of taxation for insurance companies could prevent further defections to low-tax Bermuda.

He said he was lobbying the Treasury, warning that “unless someone does something on the tax front, this slow seepage will continue”.