George Osborne has insisted the British Museum was the “victim of an inside job” following the theft of almost 2,000 artefacts.
The institution has recovered around 350 of the items dating from the 15th Century BC to the 19th Century AD which were taken.
Speaking to MPs on the Culture, Media and Sport (CMS) Committee, Mr Osborne said: “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.”
He added: “We have changed our whistleblowing code, changed our policy on thefts… tightened up security on thefts.”
Sir Mark Jones, the Museum’s interim director, announced steps to upload digitally or improve 2.4 million records to safeguard the collection at the London-based attraction.
He said: “There is a task of dealing with unregistered objects, there are about a million of those.
“There are others tasks of taking the 300,000 objects that are registered but not digitised at all and digitising them, taking the 1.1 million objects which are digitised but have no photographs and making sure that they’re associated with a photograph.
“There are levels of activities here.”
On August 16, an unnamed member of staff was sacked and the items – including gold jewellery, semi-precious stones and glass – were revealed to be missing, stolen or damaged.
Mr Osborne also said recording objects is a “complicated task” following the suggestion that the institution 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,” he said.
He added: “If someone is entrusted by an organisation to look after something and they are the person removing those objects, that is hard for any organisation, and it was hard for the museum, where there is a trusting culture.”
A Metropolitan Police investigation is under way and a man was interviewed under caution on August 23. No arrests have been made.
Meanwhile, Mr Osborne suggested the Elgin Marbles could be returned temporarily to Greece in exchange for ancient artefacts that have never been seen in the UK.
Greece has been campaigning for decades for the return of the artefacts, which once adorned the Parthenon atop the Acropolis in Athens.
The country has long claimed they were illegally acquired during a period of foreign occupation, while British officials have rebuffed repeated demands for their return.
Mr Osborne said: “We think they play a very important part at the museum in telling not just the story of ancient Athens and its role in the world but how it sits alongside other great civilisations.
“I think it’s worth exploring – and I’ve been in direct talks with the Greek government about this – is there some sort of arrangement that would allow some of the sculptures to spend some of their time in Greece? And what would be the partnership that would be born of that?”
