U.S. firm O'Melveny & Myers boosted operating profits at its London arm to almost £5 million last year – a staggering rise of more than 400% compared with the previous year.

The figures cover the calendar year 2018, described by one former O'Melveny partner as an "amazing" period for the firm.

The growth was reflected in the firm's highest remunerated member, who was allocated profits totalling £1.6 million – more than four times the previous year's allocation of £371,000, limited limited liability partnership accounts filed at Companies House have revealed.

Its London arm also boosted its revenue by almost a third to hit £15.4 million in 2018, while its cash position also grew, rising from £1.3 million in 2017 to £3.4 million in 2018.

The firm is currently seeking a new home for its London base, as its lease is ending at its current office in Paternoster Row, near to the London Stock Exchange.

A spokesperson for the firm said in a statement: "We are in the process of securing new space in London."

The strong year preceded a tumultuous period for the firm.

Several partners have left its London base so far in 2019, as its strung-out merger talks with Magic Circle outfit Allen & Overy dragged on until being called off last month.

Significant departures have included a three-partner funds team who joined U.S. rival Akin Gump this summer, while senior funds consultant Jonathan Blake also left.

Earlier this year, banking partner Sherri Snelson left for White & Case.