HMRC have recently issued guidance on the new penalty regieme for late Self Assessment returns.
You can see it here:
The new penalty regieme starts from this month, April 2011, and increases the penalties for late returns significantly:
The penalties for filing your tax return late are:
* Day one: you will be charged an initial penalty of £100, even if you have no tax to pay or you have already paid all the tax you owe
* Three months late: you will be charged an automatic daily penalty of £10 per day, up to a maximum of £900
* Six months late: you will be charged further penalties, which are the greater of 5 per cent of tax due or £300
* Twelve months late: you will be charged yet more penalties, which are the greatest of 5 per cent of tax due or £300. In serious cases you face a higher penalty of up to 100 per cent of the tax due.
Penalties for paying your tax late are:
* Thirty days late: you will be charged an initial penalty of 5 per cent of the tax unpaid at that date
* Six months late: you will be charged a further penalty of 5 per cent of the tax that is still unpaid
* Twelve months late: you will be charged a further penalty of 5 per cent of the tax that is still unpaid
These penalties are on top of the interest that HMRC will charge on all outstanding amounts, including unpaid penalties, until your payment is received.
[Source: HMRC]
Alas, this is not a April fools joke, despite the date of the post.