The lawyers acted for rugby player Paddy Jackson in the high-profile nine-week trial in which he and three others were found not guilty of raping a 19-year-old woman.

Mr Best attended court to support his former Ulster and Ireland teammate but told a radio interview in January that he regretted attending the trial.

Defamation lawyer Paul Tweed reportedly sent correspondence to Mr Best on behalf of two partners at KRW LAW LLP and barristers Brendan Kelly QC and Stephen Toal BL last month.

The matter has now escalated and a writ of summons has been issued against Mr Best, the Belfast Telegraph reported on Saturday.