A Bradford business leader is calling for an investigation into why so many entrepreneurs are failing to cope with the new self-assessment tax system.

Around one-and-a-half-million people in the region - mainly high earners and those who receive untaxed income - have to submit self-assessment returns this month.

Any who miss the January 31 deadline will face an automatic fine of £100, and could have to pay up to 6.5 per cent interest on any outstanding tax until it is cleared.

But with four million returns still outstanding nationally, chartered accountants fear more taxpayers than ever will miss the cut-off date - resulting in a multi-million pound windfall for the Treasury.

Alan Wintersgill, president of the West Yorkshire Society of Chartered Accountants and a partner in Bradford firm Naylor Wintersgill, says it is time to think again.

He said: "We are now in the fifth year of self-assessment, but the number of people who send in returns late, or not at all, is increasing and we need to know why.

"The system is very complex, which may be the reason many just don't or can't do it properly, but it's in everybody's interests that some attention is given to what's going wrong."

In the last three years, self-assessment penalties collected by the Inland Revenue have increased five-fold to more than £50m.

Taxpayers without professional advisers now have to work out how much they owe, with only the Government's lengthy Tax Calculation guide available for guidance.