On eBay? Then taxman may be on to you

Private tutors and tradesmen are also in the sights of HM Revenue and Customs (HMRC), following a series of tax amnesties over the past year.

The drive is aimed at raising 7 billion for the government during the current parliament by tackling tax avoidance, evasion and fraud.

The popularity of online marketplaces such as eBay, Amazon, Gumtree and Auto Trader has soared in recent years as the squeeze has tightened on household finances, with a growing number of people boosting their income by selling goods online.

But there are concerns that the difficulty in distinguishing between people buying and selling personal goods online and those trading for financial gain might result in some people being unfairly penalised in the crackdown to be launched over the coming months.

Gary Ashford, of the Chartered Institute of Taxation, said: "It will be important for HMRC to explain to e-traders the border line between an individual selling one's own surplus belongings and moving into trading. Individuals who think they might be trading should consider seeking advice from a tax adviser."

• Analysis: HMRC sending out a strong signal over undeclared earnings

Ronnie Ludwig, a partner at Saffery Champness in Edinburgh, said an e-trader tax evasion drive has been on the cards for some time. "Initially, it was a useful format for people to sell off unwanted gifts on a 'one-off' basis, but many people are trading over the internet with large stocks of goods and banking the proceeds in undeclared offshore bank accounts," he said.

Recent amnesties have been aimed at professionals - including dentists, doctors and plumbers - seeking to encourage those with undeclared taxable income to come forward in return for a reduced penalty.

It is not yet clear whether the latest campaigns will feature amnesties, but voluntary disclosures will earn better terms. Penalties are likely be capped at between 10 and 20 per cent of the tax outstanding, whereas those failing to come forward face fines of between 35 and 100 per cent of the unpaid tax, plus the amount owed.

People selling only a few items irregularly should not worry, said Chas Roy-Chowdhury, head of tax at the Association of Certified Chartered Accountants. But he added: "If you buy and sell through a shop you would need to pay tax, and trading online is no different.If you fall into this category, you will be far better off paying any tax owed voluntarily, rather than hoping HMRC doesn't catch up with you."

Private tutors and coaches will also be targeted by HMRC, as will any tradesmen not included in the tax amnesty for plumbers.

Ludwig believes HMRC might turn its sights not only on the tradesmen being paid cash in hand, but also those employing them. "If you get a joiner to do work on replacing your window frames on a cash-in-hand basis, HMRC may well one day decide to knock on your door for having assisted in an act of tax evasion," he warned.