MARGARET Thatcher was threatened with a fine for failing to register for the poll tax, despite making it her flagship local government reform, the newly released official documents have revealed.

The former prime minister was warned she would be in breach of the law unless she completed her registration form on time.

The embarrassing oversight – due in part to a bureaucratic wrangle between the Cabinet Office and Westminster City Council – was quickly rectified, but it marked an inauspicious start for a measure widely regarded as the biggest policy blunder of her 11 years in power – one which finally cost her the premiership.

In early 1989, as the political storm was gathering strength, Westminster City Council – like other authorities around the country – began issuing registration forms in preparation for the launch of the tax in England and Wales the following year.

It came as it also emerged that the Conservative government secretly discussed increasing the amount Scots would have to pay the community charge – widely known as the poll tax – before the levy was even introduced, newly released documents show.

A memo to the then prime minister, which was marked “confidential”, on January 25, 1989, just months before the new levy came into force, dwelled on the “long-standing” problem with business rates in Scotland, which were typically much higher than those south of the Border.

It added that the disparity would be thrown into the spotlight because England was due to introduce a “unified business rate”.

Mrs Thatcher was told that the Scottish Secretary Malcolm Rifkind would “stress the political angle: Scottish business is the Government’s main, if not only, real ally, north of the Border and at all costs must not be alienated by a failure to act”.

The note went on to say that the chief secretary to the Treasury would suggest that Scottish business rates could be cut if the poll tax, officially known as the ‘Community Charge’, was increased.