English Heritage is looking for a contemporary Croesus willing to spend up to £20 million to complete repairs to one of the grandest stately homes in England.

Apethorpe Hall, near Stamford, Northamptonshire, is built of blemishless oatmeal and honey-coloured stone, and has the timeless, ravishing beauty of an ancient Oxbridge College — Porterhouse Blue and Another Country were filmed here. The long gabled fronts, bristling with urns and chimneys, enclose one of the most graceful country-house courtyards in all England.

Apethorpe was built for a 15thcentury courtier and extended for an Elizabethan Chancellor of the Exchequer. James I commanded the Earl of Westmorland to add a long gallery for his “more commodious entertainment . . . and princely recreation”, supplying the timber from Rockingham Forest.

English Heritage has just completed an exemplary programme of repairs to the roof's stonework and plasterwork of the two main ranges. At first sight the guide price of £4.5million to £5million for 50 acres and a house of 70,000 sq ft sounds attractive, particularly as the principal rooms are of stunning quality with ornamental plasterwork as delicate as lace.

The catch is that the house will not be fully yours until you have spent a further £4million on an exacting schedule of repairs set out by English Heritage. And this is before you have introduced water, electricity and heating, kitchens, bathrooms and other essentials of modern life. “There's not a socket or a tap,” said Nick Hill, the project director.

Should you require privacy you will have to pay another £7million to £8million representing the full amount the Department for Culture, Media and Sport has spent on compulsory purchase. Otherwise Apethorpe comes with the obligation to open the house 28 days a year, though this can be in the form of pre-booked tours.

English Heritage stepped in to save the house from galloping decay. Taken over as an approved school in 1949, Apethorpe had been sold to a Libyan owner who had plans for a language college but never returned after the national outcry after the shooting of WPC Yvonne Fletcher from the windows of the Libyan Embassy in St James's Square.

The rescue of Apethorpe with public funds is down to the determination of the youthful chief executive of English Heritage, Simon Thurley, a leading expert on royal palaces who masterminded the spectacular re-creation of the Privy Garden at Hampton Court Palace. He persuaded ministers to serve a compulsory purchase on the absentee owner in Athens. Bravely he has demolished the row of wardens' houses along the back drive and classroom blocks that gave the house a depressingly institutional feel.

The chief internal glory of Apethorpe lies in the royal apartment created for James I, who came here ten times — more than to any other country house. At Apethorpe he met George Villiers, who became the first Duke of Buckingham, whose chamber connects directly to that of the king.

Here layers of paint have been removed with scalpels from the ornamental ceilings to reveal the pristine detail of flowers, fruit and heraldry. In the Great Chamber it is now possible to distinguish the 1620s plasterwork made from wood moulds and the hand-modelled 18th-century additions.

The house is surrounded by extensive lawns, a yew-lined bowling green, a sunken garden and walled kitchen garden with numerous hothouses and cold frames. There is a large stable block and coach house.

Simon Thurley is convinced that Apethorpe will find a single private buyer. Meanwhile, the public have the chance to visit the house for the next three months.

Tours of the hall take place on Wednesdays and Saturdays in June, July and August. Tickets are £7.50, pre-booking (0870 3331183) essential.

Potential purchasers should contact Harry St John at Smith Gore in Oxford on 01865 733304 or harry.stjohn@ smithsgore.co.uk.

MAKING OF APETHORPE

— Built in 1470s for Sir Guy Wolston, the constable of nearby Fotheringhay Castle

— Bought in 1551 by Sir Walter Mildmay, who became Chancellor of the Exchequer. He entertained Elizabeth I here in 1566

— Sir Francis Fane remodelled the state rooms and added a long gallery in 1622-24 for James I

— Acquired by Leonard Brassey in 1904. Sir Reginald Blomfield laid out the formal gardens

— Sold in 1949 to an approved school run by the Roman Catholic archdiocese of Birmingham which closed in 1982

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