Dechert has been dealt a blow in its long-running £16.3m fee dispute with former client Eurasian Natural Resources Corporation (ENRC), after a High Court judge questioned the legitimacy of the bill.

In the ruling handed down today, the judge said Dechert's fee estimates were "considerably awry on every occasion" and were based on "highly unrealistic" assumptions.

The ruling means FTSE 100 mining giant ENRC can proceed in its attempt to recover millions of dollars from the law firm.

ENRC has accused Dechert of "systematic and gross overcharging", after the firm billed the London-based mining company £16.3m ($20.3m) for 23 months of work relating to a criminal investigation by the Serious Fraud Office (SFO).

The dispute will now move to formal costs assessment proceedings, which an ENRC spokesman said are likely to take place at London's High Court early next year. ENRC, which is being represented by London disputes boutique Signature Litigation, is disputing £11.6m of Dechert's total fee.

A spokesman for ENRC said the company was "pleased" with the ruling. "We have always been concerned about the level of charging by Dechert, but felt unable to challenge these while our internal investigation was underway," he added.

A Dechert spokeswoman said: "We look forward now to proceeding with the costs assessment process."

The judgment [PDF] also revealed that DLA Piper, which was originally hired by ENRC to work on the internal corruption probe, had estimated that its fees on the matter would come to £350,000-£400,000 plus VAT and disbursements.

DLA's lead partner on the dispute, Neil Gerrard, took the instruction with him to Dechert when he joined the firm in 2011. Dechert was subsequently fired by ENRC in April 2013, with the company initiating proceedings against the firm that autumn.

In a letter to The American Lawyer in May 2016 [PDF], Dechert general counsel Arthur Newbold said that ENRC's allegations were "outrageous and unfounded".

Dechert had previously failed in two separate attempts to have the costs proceedings heard in public. ENRC successfully argued that a public hearing could have potentially damaging consequences for the company's ongoing SFO investigation.