When I was younger and fitter I used to play a bit of rugby union. I played in the backs and when the ball came out to us, we had one job to do, and that was to cross the 'gain line'. This would ensure that the pack was moving forwards, remained on the front foot and retained the advantage. In the game that is HM Revenue & Customs (HMRC) versus the offshore industry there have been a number of developments in recent years and it is now HMRC which is undoubtedly in the ascendancy.

There are three reasons for HMRC's success. The first is that legislation and documentation has been tightened up. Second, HMRC has enjoyed some success in the courts and, third, there has been a significant increase in the amount of funds made available to HMRC to combat tax avoidance.

On the legislative front, the tightening up began in 1998 with changes to the anti-avoidance rules that apply to offshore settlements and individuals. Perhaps most significant to individual taxpayers was the demise of 'golden trusts', a product of the late 1980s that had enabled most people, regardless of domicile and residence, to gain certain tax advantages from setting up offshore settlements.

More recently, the introduction of the disclosure rules has required advisers and promoters to disclose anti-avoidance techniques, many of which involve offshore structures, to HMRC. This enables HMRC to react more quickly to areas where tax is being lost, as recently evidenced by the removal of 'seeding relief' for stamp duty land tax purposes on the transfer of property into a unit trust, almost always offshore.

The tax law rewrite project, aimed at simplifying and consolidating the legislation, is also being used by HMRC to tighten up the law in a few places. One example is the restriction of what was known as the '741 defence,' which prevents HMRC from applying the income tax offshore anti-avoidance rules. When rewritten earlier this year, the scope of the defence was significantly curtailed.

The success in the courts has also buoyed HMRC. Some of this success has not been of its own making but has come from the criminal courts. The now well-known case of R v Allen [2001] presented HMRC with the opportunity of challenging the occupation of a home (usually by a foreign domiciled individual) if the property was owned by an offshore company. Now, particularly in light of HMRC's actions (as outlined below), such owner-ship structures should be avoided if at all possible.

More worrying is HMRC's recent success in persuading the Special Commissioners (the decisions are anonymous) to order banks to disclose to them the account details of their customers. Undoubtedly there are a number of foolish individuals who insist on holding undeclared funds offshore. There always will be. The fact remains, however, that the UK is one of the most popular tax havens in the world for individuals with a foreign connection and that the vast majority of these accounts are taxed appropriately.

This decision means that HMRC would now appear to have the ability to 'go fishing' whenever it feels inclined to do so. The concern to the correctly declaring UK resident but non-domiciled individual is one of cost.

Enquiries or full discovery assessments into offshore structured wealth are expensive and, notwithstanding their proper behaviour, clients wish to avoid this at all costs. In the past, the 'fishing capacity' of HMRC did not worry too many individuals because it was widely known that HMRC was under-resourced and did not have the capacity to use such powers effectively. That has now changed and HMRC has a bigger boat to fish with.

In 2003, the Government made £66m available to HMRC to tackle avoidance of tax offshore. Some of this money was used in 2005 for HMRC to set up the offshore fraud projects group. The Government wants to see results from its investment and gave HMRC three years (until 5 April, 2006) to raise an additional £1.6bn.

In HMRC's report for 2004-05 it was noted that the success of the team had been limited in the first few years, but that 2005-06 should see it meet its target. So what is HMRC's team doing with this windfall?

To start with, it is going through the bank details of a number of offshore account holders. Using this authority there are likely to be other disclosure orders to follow. The team is also known to be trawling the Land Registry records to establish exactly how much UK property is owned by offshore companies.

A particular concern to HMRC is the loss of inheritance tax that may be arising as a result of ownership through offshore structures, although the 'deemed emolument' issue is one which also interests HMRC in light of Allen.

There is, however, one major change to HMRC practice which threatens to over-shadow both of these intrusions into a client's affairs. The 2005-06 self-assessment return has, arguably, changed the manner of disclosure for foreign individuals who are relying on the remittance basis of taxation.

Previously, one simply ticked the nondomiciled box in the foreign pages and did not mention foreign income that was not remitted to the UK (although many changed their practice after the Veltema case). The self-assessment return and guidance notes have changed for 2005-06. There are conflicting views on the new requirements of the taxpayer, but one view (with which I do not agree) is quite worrying. This is that it is now necessary for the individual to declare in the 'additional information' box that he or she has foreign income that has not been included in the form.

It follows that HMRC will have to enquire into every return filed in this manner this year because failure to do so after such a disclosure would otherwise be confirmation that foreign domicile and the remittance basis of taxation is accepted. This is the view put forward recently by a number of professionals in tax journals and, if correct, has the potential to overwhelm HMRC.

The long and the short of all the above is that HMRC has access to more information than ever before about the offshore affairs, structures and accounts of individuals and now also has the funding required to scrutinise that information more effectively. The expressed intention is to catch the individuals who use such accounts and structures to evade tax.

There is little doubt, however, that HMRC is information gathering on those individuals who are legitimately using such structures to mitigate their UK tax exposure and who will undoubtedly come under closer scrutiny in years to come.

Returning to the analogy of the rugby pitch and the backs putting the forwards on the front foot, it would appear that HMRC is on the attack and is advancing up the pitch. The only point it should be wary of is that there is still one large obstacle between it and its objective. Many of the UK's anti-avoidance rules are thought to be contrary to the laws of the European Union. It is a matter of when, not if, there is a challenge on this basis. If successful, HMRC could find itself losing a huge amount of territory in what could be a large blow to the team.

Richard Jordan is a partner in the tax and trusts department at Stevens & Bolton.