Bird & Bird has replaced Deloitte as the firm's auditor with rival accountant Grant Thornton.

Deloitte had held on to its auditor role the last time a formal tender was carried out four years ago, but it filed a resignation notice at Companies House last month to confirm the termination of its position.

In the notice Deloitte, which expressed its willingness to continue as Two Birds' auditor in the firm's most recent accounts, said there were "no circumstances connected with" its resignation that it "considered should be brought to the attention of the members or creditors" of Bird & Bird.

However, Deloitte have been retained by Two Birds to provide tax advice.

The firm spent £273,000 on tax services in the year to 30 April 2014 – the most recent year for which it has filed accounts.

Bird & Bird also paid Deloitte and its associates £272,000 in audit in fees in the same year.

Two Birds said that "the reasons for the change should not in any way be perceived as dissatisfaction with Deloitte's work" and that it was "healthy for the business to change auditors periodically."

The chief financial officer at one top 20 law firm said "a lot of consultants are being more commercial" about their relationships with law firms than in the past.

He added: "They think can get more money out of advising than they can out of audit."