Two civil servants who have refused to name the source of a document containing the names of hundreds of people with illicit bank accounts abroad are within their rights not to do so, the advocate-general says in his advice to the Supreme Court.

The list led to 61 people with money in various bank accounts in Luxemburg being fined for hiding their savings from the Dutch tax authorities. Tax lawyer Mark Hendriks is fighting the fine for several account holders and wants the name of the source.

The civil servants were earlier ordered to come clean by the lower courts but have refused to state the source of the information on finance ministry instructions. It is unclear when the Supreme Court verdict is due.

The case dates back to 2009 when then junior finance minister Jan Kees de Jager bought a list of people with secret foreign bank accounts from an anonymous source.

The finance ministry has collected an estimated €1.6bn in back taxes and fines from people with secret bank accounts abroad.

The ministry said in a reaction to Monday’s ruling it is ‘a major bonus’ that civil servants have the right to refuse to answer questions.