THE biggest fire for a decade which raged across Dartmoor on Wednesday is being treated as arson.

'We believe it was started deliberately,' said Robert Steemson, head ranger for Dartmoor National Park Authority. 'By whom we have no idea. But fires like that don't start on their own.'

The blaze is thought to have started at Ryders Hill, the highest point of the southern moor, near Holne.

But soon after the emergency services were alerted from the Newton Abbot end at 9.30am, the huge blaze was also reported from Princetown.

'At first we thought it was two incidents,' said Ann Moore, from the Devon Fire and Rescue press office in Exeter. 'But it grew to such an extent it turned out to be the same one.'

At its height it spread across a ten mile section of the moor and 60 firefighters were tackling tinder-dry gorse.

Two firefighters had to be helped from the scene suffering from heat stress – one of them was airlifted out by police helicopter.

'The fire service was at full stretch, but we had it all covered,' Mrs Moore said.

The Holne Commoners Association also helped fight the blaze and did what Mr Steemson described as 'a sterling job'.

Park rangers brought in a special 'fire fogging' device from Okehampton capable of picking up water from Dartmoor streams and dispersing it in a fine spray.

The flames have put at risk a special blanket bog conservation area about which Dartmoor Rangers were already concerned after six weeks of dry weather.

Yesterday, Rangers were carrying out a special check to see how bad the damage was.

Police would only say they are treating it as 'suspicious' after reports that two men on quad bikes had been seen in the area.

They closed roads in the Two Bridges area and told walkers to stay off the moor.

Some students carrying out a Duke of Edinburgh award scheme were among those asked to leave.

At one point ramblers hoping for a close view of the blaze tried to head straight for its heart, an action which police described as 'extremely dangerous'.

Fire appliances from all over Devon were called to the scene.

after an all day battle, the blaze had been confined to one front by 6.30pm – although there were still substantial hotspots.

Overnight rain helped to damp down the blaze and by yesterday morning all fire appliances had been withdrawn.