By Paul Lewis
BBC Radio 4's Money Box
MPs and other high profile individuals cannot file their self-assessment tax forms online for security reasons, it has been revealed.
If your tax number has 11 digits, then you will have to use paper
The Revenue says some people have an extra digit in their tax number showing they have personal security issues and their files are held separately.
They cannot file online because the computer system will only work with the standard 10 digit reference number.
The Revenue says the problem is being addressed and online filing is safe.
Andrew Goodwill, director of the internet security firm, Third Man Group, told Radio 4's Money Box programme that he did not believe this explanation:
"All outward signs look as though it is secure.
"But that would suggest that the systems behind are not as secure as they might be.
"It would be astounding that they have spent millions and millions of pounds on a system that cannot cope with a longer number.
"It is possible it is a smoke-screen."
Andrew Robathan, Conservative MP for Blaby, who raised this issue in the House of Commons, agreed:
"I am not quite sure I buy that explanation - I am concerned about the security of data in the hands of government.
"This has huge implications for everybody who files a tax return.
"The big issue is whether the data of all my constituents is safe.
"I will be taking this up with the information commissioner."
John Whiting, a partner with accountants PricewaterhouseCoopers, says extra security has long been applied to some tax forms and that might be indicated by the extra digit.
"Back in the days of paper returns some were treated specially - the Queen's for example and the prime minister's.
"And certain people have not been able to file online - those with complicated capital gains, for example.
"And, we were always told, MPs because of their allowances.
"Now we are being told something different.
"You can understand the Revenue wanting to add extra security when the information gets to them."
A spokeswoman for Her Majesty's Revenue & Customs told the BBC, "Particular people have always had enhanced security by the nature of their work.
"They have had an additional digit for more than 30 years to indicate that.
"The online system does not recognise the extra digit - it is only geared for 10 digits and they have 11.
"We are working to find a way round it.
"That will not give them enhanced security because it is already very secure - it won an award for its security."
BBC Radio 4's Money Box was broadcast on Saturday, 26 January 2008 at 1204 GMT.