The JCB has been used for lifting and moving huge rocks around the site to create what will be called The Lion Country.

Operations director at the park, Neville Williams, said work on the enclosure had been delayed by the cold winter, and was now going to be May.

He said the enclosure would be surrounded by banked walkways which allow visitors to look down into the cage. There will also be a bridge over the lions' home.

The three prides of lions will be kept apart by lakes.

Mr Williams said: "We think the way people will be able to see the whole of the Lion Country will be unique in the UK.

"We have seen great improvements in the condition of the lions. A lot of their sores they had when they arrived have cleared up and they're on a good red meat and supplements diet. The vets are delighted with their progress.

"They are getting vocal now which is a good sign that they are settling in. I never tire of hearing the lions roar."

He added when work was complete, it would be the first time the lions had trodden on grass.

The lions' enclosure will be bounded by a four metre high fence and a ditch.

The lions were rescued from a run down zoo in Romania where they faced an uncertain future living in inadequate facilities. They were flown to the UK to start a new life at the park. Believed to be the largest big cat rescue ever, park directors initiated a campaign through the charity Wildlife Heritage Foundation to raise £150,000 to save the lions back in August after learning of their plight at Oradea Zoo.

The park's contractor, North Eastern Plant, brought in a JCB JS460 tracked excavator, weighing in at 46 tonnes, to unload and position up to 10 large rocks weighing 12 to 20 tonnes.

When positioned the rocks will act as a lounging area for the lions as well as support to a waterfall feature also currently in construction.

North Eastern Plant boss Jim Turner said: "The JS460 is proving an essential piece of kit to enable us to safely and efficiently move the enormous pieces of stone into position and further develop the area for the lions."