The big, bad, tax man is out to get you, self-assessment taxpayers have been warned.
Some face an increased risk of being investigated by HM Revenue and Customs, claims accountants Grant Thornton.
The concern comes as the annual scramble to file gathers pace.
Gary Ashford, tax investigations senior manager at Grant Thornton's Birmingham office, said: "Self assessment is becoming increasingly complicated following recent tax cases and the growing complexity of legislation.
"There has been a sharp increase in the amount of investigations conducted by HMRC over recent years.
"In 2004/05 the amount recovered from those self assessing was up 17 per cent on the previous year, a result of much higher HMRC targets. Inspectors will again be looking closely for any errors on submitted tax forms, which could prompt investigations. I would urge individuals to take extra care when filing their forms due to this increased scrutiny."
HMRC's recent annual report and accounts revealed it collected £249 million from enquiries tackling noncompliance from individuals who self-assessed in 2004/05, up from £212 million in 2003/04.
One of the reasons for this increased effort and yield return is a three year Government initiative, launched in March 2004 and costing £115 million, in which HMRC committed to recover £2 billion over the three years 2004/05 to 2006/07.
Mr Ashford continued: "Don't forget that even if you have not been sent a tax return by HMRC, you are obliged to tell them if you have acquired a source of income - for example rental income, or income from investments or self employment - or if you have made a capital gain, which makes you liable to tax.
"Such notifications should have been sent to HMRC by October 5, 2005 but a late notification is better than no notification."
A recent change in policy by HMRC not to issue receipts for self assessment forms delivered by hand, may be bad news for those who leave filing their forms to the very last minute, as they may not have evidence of delivery to avoid a late payment penalty.
Eric Williams, Grant Thornton's Birmingham head of tax, said: "HMRC originally said it would accept 'reasonable evidence', without saying what this includes.
"It has now issued guidelines, but I would recommend people file online, where possible, as this enables electronic receipts to be issued automatically."
Hand delivered returns should be accompanied by a list, date stamped for the relevant date of delivery, and listing the name and Unique Tax Reference (UTR) of the return. A copy of the list should be retained in case of subsequent problems - Royal Mail offers an online "track and trace" facility with its special and recorded delivery services Mr Williams went on: "If returns are not received by February 1, there is an automatic £100 penalty.
"In addition, the Revenue can ask the Appeal Commissioner to impose hefty fines of £60 per day until the outstanding bill has been paid. Last year, HMRC issued 37,464 such charges, amounting to £110 million.
"This year HMRC has been set a target of 93 per cent of all self assessment forms to be received on time, and with a million of the simpler returns taken out of the system, this will be a tough target. Coupled with a recent report into self-assessment, there is a growing trend that fines will be levied more aggressively."