500,000 face tax penalties if they don't pay up by Tuesday

Taxpayers who didn't file their returns in January face another £100 fine and a further penalty based on how much they already owe if they miss this week's 31 July deadline.

More than 11 million people – including higher- rate earners, workers with sources of untaxed income and the nine million self-employed – have been issued with return forms by Revenue and Customs for the tax year ending 5 April 2006.

However, nearly a million of them failed to get their forms in by 31 January this year and picked up a £100 fine.

It is estimated that around half of this group have still to pay up and are on track to be hit with more, and heftier, penalties if they miss Tuesday's deadline: another £100 and a rise in the penalty on outstanding tax to pay from 5 to 10 per cent.

Anyone in difficulty with their self-assessment form can get help from a special phone line, 0845 900 0444, or go to www.hmrc. gov.uk/sa/sevens.htm

After 31 July, the next deadline to watch out for is 30 September.

Those completing a paper tax return for the 2006-07 financial year must send their form back by this date if they want Revenue and Customs to calculate their tax, work out what to pay by 31 January 2008 and collect tax through their tax code, if possible, where less than £2,000 is owed.

Remember that if you send back your tax return over the internet, the software on the Revenue and Customs website will calculate your tax liability for you.