Dartmoor's already controls 8.5m shares, a stake of 7.01 per cent.
He points out that while Sphere has an international general portfolio, Dartmoor's portfolio of mainly highly-geared instruments is not such a safe prospect.
This would give Dartmoor 52.46 per cent of the shares, but the acceptances are not yet irrevocable. The bid is only for one class of share - income and residual capital - and the warrants.
After 182 years as an all-male preserve, grim, high-security Dartmoor Prison has appointed a granny and a nanny as its first women guards.
But Mellor described the Dartmoor disturbances as "a copycat incident" in the wake of the Strangeways riot.
Those game, fierce fellows of Exmoor and Dartmoor still thrive. There are sanctuaries elsewhere in Derbyshire, Yorkshire, Northumbria and Shropshire.
May said the prisoners at Dartmoor were protesting prison food and their isolation from their families.