Alistair Darling’s capital gains tax rules became further mired in controversy yesterday as it emerged that directors of newly quoted companies could rush to dump their shares over the next six months once the lockup on their holding expires.

The revelation puts further pressure on the Chancellor to reconsider his changes, which will increase capital gains tax (CGT) in some cases by 80 per cent to a flat rate of 18 per cent.

Tax experts gave warning that a rush of sales by directors could lead to investors having a distorted view of the market. Directors’ dealings are closely watched as an indicator of their commitment to their company.

Alex Henderson, tax partner at PricewaterhouseCoopers said: “This is clearly another unforeseen consequence of the CGT changes; I suspect it’s not going to be the last.

“The general public will need to be wary when they see directors’ dealings in the run up to April 2008. It may be that directors have been motivated by the change in tax rate to sell their shares when, all other things being equal, they would not have taken the commercial decision to sell.”

Top of the likely list of early sellers are staff at BlueBay Asset Management, the fixed income fund manager that listed on the London Stock Exchange’s main market a year ago next month. At the time of the listing, staff agreed to lock into their holdings over the next four years, with the right to sell a quarter of their ownership coming each year.

Almost all BlueBay’s 190 staff own shares, including Hugh Willis, the chief executive, and Mark Poole, the chief investment officer. A spokesman for BlueBay, which posted a healthy increase in funds yesterday, declined to comment on whether staff would sell next month but acknowledged the implications of the tax measures. All companies that have listed over the past 12 months are likely to face the same issues with directors’ lock-ups.

The Treasury said: “The CGT regime has encouraged investment and enterprise. The reforms the Chancellor announced will make the system more straightforward and sustainable, ensuring it sets consistent incentives for investment, while retaining incentives for enterprise and ensuring it remains competitive internationally.”

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