The French authorities have taken firm action this year to penalise expatriates in France who have not declared their interest earnings in overseas bank accounts.

We have pointed out before in these pages that there are increasingly few places and even fewer savings or investment products that escape the prying eyes of the French tax authorities.

Like most of their European cousins, for several years now tackling tax evasion has been a major priority of the French government, with a range of new laws, practices and sanctions in place.

The government are helped in this quest by the growing obligations that exist on financial institutions and professionals to disclose information about their clients.

Perhaps the most notable of these developments in recent years has been the European Savings Tax Directive, dating originally from 2005, under which the signatories agreed to exchange information about customers who earn interest in one country, but live in another.

These arrangements have been substantially reinforced of late, for last month the European States agreed to strengthen the existing arrangements, which was followed later by a broader agreement involving over 90 countries who agreed to the automatic exchange of information, based on an OECD 'global standard' template.

This means that by 2017 all bank accounts in Europe and in many other countries of the world will be available for perusal by the tax authorities in the signatory countries. In short, the exchange of information will soon become the norm.

The extent to which the authorities in France currently rummage through the existing information that is provided has always remained unclear, but reports suggest that the computerised information now available to the French tax offices is substantial and easily accessible.

Indeed, on the evidence of the reports we have received this year, the framework now appears to be in active use, for we have received a number of enquiries from you over the past few weeks questioning the taxation in France of Individual Savings Accounts (ISAs) held in the UK.

This savings product has been around since 1999 and many British residents hold considerable savings in them.

Although expats in France can add no more to their UK ISA, they are still able to earn income, free of UK taxation. Indeed, there is no need to even to declare the sums earned to HMRC.

In all cases, these ISAs were assumed by the readers who have contacted us to be tax free in France, in the same manner as they escape taxation in the UK.

Unfortunately, that is not the case, for in France your worldwide income and capital gains is liable to tax and no recognition is granted to the HMRC tax concessions that is afforded to UK resident ISA holders.

If you have not disclosed the interest (or dividends) earned in your ISA account on your French tax return, you may find you will be taxed and fined on the undeclared income.

In some of the cases that have come to our notice, this has actually what has occurred, with a tax rate, including social charges, of up to 60% on undisclosed interest.

These charges included a fixed taxation of 40%, social charges of 15.5% and interest of around 5% on late settlement.

The sanctions are as high in those cases we have seen as the accounts have simply not been declared to the French tax authority.

The information about such accounts would have become available to the tax authorities through the disclosure obligations under the Tax Directive.

For those looking to relocated to France with ISAs one investment strategy is to dispose of your savings before you relocate, and consider taking out a tax-efficient investment product in France, such as assurance vie, or investment in a Société Civile de Placement Immobilier (SCPI).