Reeds Solicitors, a Sussex-based personal injury (PI) firm, is suing Norwich Union for an alleged breach of contract.
The firm launched its claim after Norwich Union closed its subsidiary Hill House Hammond (HHH) to new business.
Reeds claims that it had committed to an exclusivity agreement with HHH subsidiary BTE Lawline, whereby the firm would carry out PI claims work only for BTE.
The five-year agreement was signed in 2003. According to the witness statement of Reeds founder Chantal Reed, the number of cases referred to Reeds initially grew each month.
Reed alleges, though, that once HHH was closed, the new referrals stopped and Reeds was left only with existing cases. The firm says that because it is still bound by the exclusivity agreement, it is unable to seek new clients and new sources of work.
In January, Judge Hughes QC in the Queen's Bench Division struck out the majority of Reeds' claim, but on 7 March the Court of Appeal found that the case should be heard at trial. A mediation attempt failed on 18 March, leaving the parties with no option but to go to trial in April.
Reed said in a statement: "We are, naturally, extremely disappointed, but not entirely surprised that we have to proceed to court to recover the serious business losses caused by their breach of agreements."
Norwich Union declined to comment.
Reeds instructed Ashley Underwood QC of Two Field Court in the Court of Appeal, while Norwich Union's in-house team instructed Serle Court's Alan Boyle QC.