The former chancellor said a "lot of steps were taken to conceal" the alleged thefts and lessons will be "learnt".

He was speaking to MPs during a session before the Culture, Media and Sport Committee.

In August, it was revealed an estimated 2,000 items were missing - but Mr Osborne suggested the museum did not have a complete catalogue of everything in its collection.

Items, including gold jewellery, semi-precious stones and glass, were found to be missing, stolen or damaged.

Mr Osborne told MPs: "We were the victims of an inside job by someone, we believe, who over a long period of time was stealing from the museum and the museum put trust in.

"There are lots of lessons to be learnt as a result of that, the member of staff has been dismissed by us.

"The objects have started to be recovered… we have changed our whistleblowing code, changed our policy on thefts… tightened up security on thefts."

Mr Osborne also said recording objects is a "complicated task" after the suggestion the museum did not have a complete catalogue of everything in its collection.

"Quite a lot of steps were taken to conceal (thefts)… a lot of records were altered and the like," Mr Osborne said.

Read more:
Have you seen these? Museum's lost treasures
British Museum's new interim boss announced

British Museum interim director Sir Mark Jones was also appearing before MPs.

In a statement, Sir Mark said: "Following the discovery that objects have been stolen from the collection, we have taken steps to improve security and are now confident that a theft of this kind can never happen again."

On Wednesday, the London-based museum said 2.4 million records will be uploaded digitally or improved to safeguard the collection.