People who own shares in their own company could be in for a surprise when they come to sell, says an Oxford accountant.

The latest Tax Bulletin issued by the Inland Revenue has thrown light on the complex rules surrounding taper relief - the relief against tax payable when you cash in business or personal investments such as shares, said Ray Thomas, tax partner at Grant Thornton.

He said many unwary investors believed that once they have held on to a "business" investment for four years, the tax on the net gain is ten per cent. In fact, this privilege is reserved for those who successfully negotiate a series of potential pitfalls.

"Taper relief isn't something you can put right when you reach the point of trying to sell. It takes careful forward planning," he said.