Wildenstein and two family members, as well as their financiers and lawyers, were accused of deliberately understating to tax authorities the real value of family riches inherited about a decade ago and placed in trusts abroad.

The trial concerned more than 500 million euros of various goods and prosecutors asked that Guy Wildenstein, 71, get two years in jail and a fine of 250 million euros (218.89 million pounds) if convicted. The other faced various similar charges, including complicity in fraud.

The case did not produce a guilty verdict because France's tax legislation at the time lacked clarity on the declaration of inheritance assets parked in financial trusts, the court said.

The law was amended in 2011 to close this loophole.

"The court is perfectly aware its verdict may run counter to public belief and be misunderstood," judge Olivier Geron said.

He said it seemed clear there was an effort to hide assets, but the way it was done was not technically illegal at the time.

Prosecutors accused Wildenstein of deliberately failing to report the full extent of riches inherited from his father Daniel Wildenstein, who died in 2001, and after the death of a brother, Alec, a few years later.

Defence lawyer Herve Temime said the verdict was "perfectly logical" under the law at the time. "Judges can't replace lawmakers", he said.

(This story corrects number of family members and prosecutor's request.)

(Writing by Brian Love; Editing by Tom Heneghan)

By Chine Labbé