A farmer is considering putting up a substantial' reward to help catch arsonists who set light to tractors and agricultural machinery, causing almost half-a-million-pounds worth of damage.

David Morgan, managing director of Field Farm in Netherton Road, Appleton, near Cumnor, said: "This was a totally senseless act that could have killed people. They used petrol incendiary devices underneath two large tractors to set off the fires and the fuel tanks exploded.

"The tractors were destroyed and other expensive farm equipment was badly damaged.

"Fortunately the compound was isolated and no-one was hurt - but the results could have been fatal had anyone been close by. It's madness. I wonder if people realise the consequences of their irresponsible behaviour.

"This is not the first time our farm has been hit by vandals and fires. I have no idea who's behind these attacks and so I am considering offering a substantial reward to try to help catch the culprits."

Mr Morgan's son Danny, who lives on the farm, spotted the fire at about 10.45pm on Sunday. He believes he disturbed the intruders and saw people running away.

Eight fire crews were sent to tackle the blaze. They did not leave the farm until 6.30am on Monday.

Mr Morgan senior said: "Thanks to the quick work of the firefighters the blaze was contained to the machinery - although we lost about 200 tonnes of hay bales. We did not have to move the cattle from the livestock buildings but it must have been very distressing for the animals inhaling smoke."

Det Insp Chris Biddle said there was nothing to suggest animal rights activists were involved - although it could not be ruled out.

He said: "We are treating this as a very serious incident. It caused a substantial amount of damage and was potentially life threatening. "

Mr Biddle urged anyone with any information about the incident to call the police on 08458 5055505 A factory fire could be seen several miles away - as two tons of burning magnesium lit up the night sky.

Reports of the blaze at Banbury's Alcoa plant, which started at 10.15pm on Sunday, came from Bretch Hill, Easington, Grims- bury, and villages including Drayton, the Bourtons and Middleton Cheney.

Six fire engines and more than 30 firefighters from Banbury, Deddington, Hook Norton and Brackley were joined by the incident support unit and the environmental protection unit.