Broker Howden focuses on specialty commercial risk and reinsurance, while A-Plan, which sells insurance through brands including Endsleigh, focuses on personal and commercial lines such as motor, home and business liability.

The combined business will have more than 4 billion pounds ($5.1 billion) in gross written premium, the firms said in a statement.

Insurance brokers small and large have been consolidating in recent years. Aon is in the process of buying Willis Towers Watson for $30 billion to form the world's largest insurance broker.

Howden, CEO of Howden parent Hyperion Insurance Group, told Reuters that given "what our clients require in terms of servicing, data technology... there's no doubt that the combined (Howden and A-Plan) businesses will be stronger together".

A-Plan is part-owned by employees, but the majority stake was previously held by HgCapital Trust.

Carl Shuker will remain CEO of A-Plan, reporting to Jose Manuel Gonzalez, CEO of Howden.

($1 = 0.7852 pounds)

(Reporting by Carolyn Cohn; Editing by Jan Harvey)