Your friend has two options.
He could, as you suggest, sell the aircraft to "his" limited company. Since the company now owns the aircraft, the company would meet all the cost associated with maintaining and operating the aircraft. The company would be entitled to deduct these costs from its profits and would be entitled to recover some of the input VAT suffered. The company would be entitled to claim an allowance on the cost of the aircraft against it profit and on the loss, should this arise, on eventual sale. The company would be liable to tax on a profit on sale. Your friend would be liable for a personal tax liability on the private element of his use.
Alternatively your friend could charge "his" company for the commercial cost of the business element useage of the aircraft. Your friend would in these circumstances be personally liable for the maintenance and operating costs of the aircraft.
Your friend will need to consider the advantages and disadvantages of each of these options. Of course as other contributors have said he should take specific professional advice.
AIC white 21/2000 covers the restrictions applicable to an aircraft owned by a limited company in the circumstances outlined. If you wish to email me I am happy to provide a copy.