Mr Bunker said the clean up would cost up to �4m

"We have now identified the seat of the fire which we know went up very quickly and arson is being investigated as a possible cause."

The organ casing and one of the cathedral windows were extensively damaged.

Mr Bunker said the widespread smoke damage inside the building would require extensive repairs to the ornate interior which would cost up to �4m.

"The fire must have been absolutely terrible but the fire brigade got here in time thankfully.

"If they had got here 15 minutes later we could have been looking at the sky rather than the ceiling."

'Amazing coincidence'

Crews were called to the cathedral at 1840 GMT after verger Nigel Long spotted the flames at one of the cathedral windows.

He dialled 999 before the cathedral fire alarm sounded.

Fire crews put out most of the flames in 25 minutes but it took more than two hours to ventilate the building because of the heavy smoke.

Ray McDonnell, of Cambridgeshire Fire Service, said it was lucky the verger was passing.

"The coincidences that led up to the verger putting that call in were amazing.

Massive cost

"Speaking to him, he wasn't even supposed to be there.

"He saw the flickering flames from the window and without that call then we would have lost this pride and joy of Peterborough."

Heavy smoke filled the building

Mr Bunker said the nave ceiling was undergoing restoration work costing one and a half million pounds.

It is thought the cleaning work will now have to be re-done.

Brian Long, treasurer of Peterborough Cathedral Trust, said: "It is not only a disappointment to us at the trust but to those people who supported the appeal.

"The bulk of the losses we expect to be covered by insurance.

"There are things that need to be done straight away like cleaning and making the cathedral usable.

"We are determined to get the place back into working order and to recover from this."

He said the staff Eucharist had gone ahead as usual on Friday morning and said it was expected that Sunday services would go ahead.

No injuries

The fire service said the spread of the flames through the ancient building was only prevented because the blaze was discovered quickly and tackled effectively.

One of the choir stall carvings

The building had been locked when the fire was discovered and no one was injured.

Neil Thompson, spokesman for the fire service, said the damage has been kept to a minimum.

"I'm sure there has been damage to the ornate wooden carvings but it could've been far more serious."

Ancient site

Extensive smoke damage will have been sustained through the building, he added.

A total of 11 fire engines, with about 60 fire fighters, went to the scene.

The Cathedral Church of St Peter, St Paul and St Andrew is the third abbey to stand on the site.

An abbey founded on the site in AD655 was destroyed by the Danes, reconstructed in 972 but burned down by mistake in 1116.

Work on the current building started in 1118 and took more than 120 years to complete.

Notable features include the West Front, built in the 13th Century, and the tomb of Henry VIII's first wife, Catherine of Aragon.

It was also the former final resting place of Mary, Queen of Scots.