Nobody knows how much money is needlessly handed over to the taxman every year but it is widely accepted that the 180m refunded to 700,000 taxpayers in recent years is just the tip of the iceberg.

After years of ignoring the problem, the Revenue has finally been shamed into action, launching a 400,000 campaign last week to encourage more of us to step out of the shadows and claim what is rightfully ours.

PAYE workers, the bedrock of the income tax system, have the most to gain. Because responsibility for calculating and paying tax is taken out of their hands, PAYE earners typically have no idea how the system actually works. So they fail to claim for basic reliefs such as those for medical and dental bills, flat-rate expenses related to their employment or rents paid to a private landlord.

The self-employed are a lot less likely to overpay because, if their accountants are on the ball, they will have claimed all of the relevant allowances when filing their annual tax returns.

If ignorance keeps us from claiming our full entitlements, fear is the reason we do nothing about it when the overpayment comes to light. Most sensible people prefer to keep their dealings with the Revenue to a minimum. After all, what is the point in chasing after tax relief for trade union subscriptions, which will save you at most 60 a year in tax, if it prompts the taxman to take a more active interest in your affairs? The Revenue insists we have nothing to fear . . . provided of course we have nothing to hide.

"All we want to do is ensure people are paying their fair share, and the right amount, of tax, " says assistant secretary John Leamy. "There's still a fear about approaching the tax office. It's totally wrong because the services we provide are totally removed from the compliance side.

Obviously we police some claims to ensure there's no fraud, but this is a really serious effort to tell people what they're entitled to."

These assurances are unlikely to convince anyone caught up in the high-profile Revenue investigations, which have yielded a 2.2bn windfall for the exchequer in recent years.

Almost all of these people knew they were bending the rules when they gave false addresses to open bogus nonresident accounts or stashed hot money in the Isle of Man or the Channel Islands. But they never suspected that the Revenue had the wherewithal, not to mention the political backing, to do something about it.

Having flexed his muscles to such dramatic effect, it will be interesting to see how the taxman copes with his new role as a benevolent public servant, fretting that some home-owners might have overlooked tax relief on their bin charges.

Even if we pluck up the courage to contact the local tax office, other terrors lie in store, according to the Institute of Chartered Accountants.

It accuses the Revenue of being "uncontactable by phone for weeks at a time" and, even when callers manage to get through, their queries are often not followed up.

According to the accountants, "Revenue need to improve their customer service standards and ethos if compliant taxpayers are to get a fair deal".

The good news is that most people will shortly be able to bypass the phone and manage their tax affairs online. The selfemployed have already embraced the Revenue Online Service (ROS) to pay and file their tax using the internet. A similar facility is now being extended to PAYE workers and they are being sent passwords that will allow them to undertake basic functions, including claiming tax allowances and credits, by internet or mobile phone.

It's is a welcome alternative for anybody who has ever queued in a tax office or spent a morning getting an engaged tone from a Revenue helpline. But even the best technology is prone to gremlins and ROS has a habit of crashing right on the payand-file deadline, just when taxpayers need it most.