HM Revenue and Customs, the UK tax authority, made 640 requests for information on individuals’ tax affairs to overseas governments in the 2011 to 2012 tax year, according to the latest research from international law firm Pinsent Masons.

The tax requests were made under “double taxation agreements” - these are mechanisms designed to prevent an individual’s income or assets being taxed in two different countries, while also providing tax authorities with information regarding the value of assets an individual has declared overseas, helping the authorities assess the tax liability of that individual in their “home” tax jurisdiction.

The UK, along with other nations, has sought to crack down on tax evaders’ use of offshore accounts, signing exchange of information agreements and other pacts in recent years. For example, the UK has signed a bilateral treaty with Switzerland to uncover hidden wealth.

Continuing the expansion of this network, last year HMRC signed new agreements with Barbados, Liberia, Brazil and Grenada, among others, the law firm said.

“Taxpayers hiding assets from HMRC overseas are running out of places to hide. HMRC will use every tool in its arsenal to find out where people have assets,” said Phil Berwick, partner at Pinsent Masons.

“It is far better to get on the front foot and tell HMRC about an undisclosed offshore asset or other problem before HMRC finds out and begins an investigation. There are various mechanisms people can use to report their undeclared overseas funds and assets to HMRC, so there really is no excuse not to,” said Berwick.

Countries targeted by HMRC in 2011 included Australia (96 requests), Spain (49 requests) and Ireland (38 requests).

Additionally, HMRC received a list of HSBC customers with offshore accounts in Jersey from a whistle-blower, demonstrating the breadth of sources available to HMRC in its pursuit of missing taxes, Pinsent Masons said.

However, since the 857 requests made in 2010, there has been a 40 per cent decline in the number of HMRC requests in the last tax year (2011-2012). The HMRC said it has “picked off most of the low-hanging fruit”, highlighting that attentions are being turned on wider and more complicated cases.