Buckingham Palace turned to City firm Herbert Smith rather than Farrer & Co for an injunction against the Daily Mirror last week to stop it printing material obtained by an undercover reporter.

The fact that Farrers, the Queen's usual law firm, was not used in a case involving the media - one of its specialities - surprised commentators.

However, a Buckingham Palace spokeswoman said it was not the first time Herbert Smith had been used: 'They [Herbert Smith] cover different areas of law for us.'

She also confirmed that costs in the case will be paid by the Royal household, even though the Queen is represented in personal court proceedings by the Attorney-General.

She said: 'Taxpayers' money will not be involved in any payment of legal fees over and above the Daily Mirror's contribution.'

The Daily Mirror this week agreed not to print any further details and to contribute 25,000 to the Queen's legal costs.

However, this is unlikely to cover the total now owed to Herbert Smith and David Pannick QC and Jonathan Sumption QC, estimated by some at 70,000 to 100,000.

Neither firm wished to comment.

Jeremy Fleming