Arthur J Gallagher (UK) achieved 70% growth in pre-tax earnings last year.
The UK operation of the world's fourth largest broker reported top-line brokerage growth of 55% in the same period.
Managing director Brian King said company expansion had been rapid.
"There has been a strategy in the UK to grow both the presence and the capabilities of the London operation," he said.
"Areas of expansion included aviation, construction, energy, political risks and fine art and specie."