This acquisition marks another important step in the firm’s ambitious buy and build programme since it joined private equity backed Sumer Group in December 2023. This is the second M&A deal of the year focused on London accountancy firms with revenues around the £2m mark.

Founded by John Riordan in 1968, Riordan O’Sullivan & Co is based in north-west London and operates as a traditional partnership, not an LLP, and is an ACCA accredited firm, offering tax, audit and accounting services to a range of clients, including family-owned businesses and entrepreneurs. 

The three partners, James Riordan, Paddy McNamara, and Kumar Perumal plus 16 professionals will join the Sumer group business.