Terra Firma is gearing up for a bruising legal battle with its former banker Citigroup. The case has involved high-profile litigants, juicy troves of documents, court appearances on both sides of the Atlantic and most importantly for the lawyers involved – giant legal fees.

All in all, it should be a trophy case for any law firm with a decent litigation practice. But in 2011, when Terra Firma, a private equity firm based in London, began to mention the case to solicitors who had done other work for it, a strange thing happened. None of the big firms it approached would touch the case, according to a person familiar with the matter.