Cherie Blair, the wife of former British Prime Minister Tony Blair, is taking on a big legal challenge. She’s representing Mikhail Fridman, a wealthy Russian businessman, in a lawsuit against Luxembourg. This case is all about Fridman’s assets that were frozen because of European Union (EU) sanctions. Last month we informed you about another such case where UniCredit and Raiffeisenbank have taken the Central Bankers to court over Russia sanctions.

Mikhail Fridman, who founded Alfa Group,...