First a confession. I am about to extol unreservedly the considerable virtues of Wallington in Northumberland.

I'm not by nature a devotee of aristocratic mansions. No aspect of contemporary behaviour, it seems, is as entrenched as the cult of the country house, mellow, Millaised, Morrissed, and maintained in perpetuity by the National Trust. I did not, therefore, mourn the sale of Mentmore to transcendentalists, nor spare more than a single tear when Madam Tussaud's captured Warwick Castle.

It is the nature of history that ancient properties are built, rebuilt, restyled or demolished by generations of owners. And when one considers the horrors that are created with massive public funds by traditional owners - witness the economically successful vulgarities of the water gardens at Alnwick - who are we to laud as the custodians of culture, or brand as barbarians?

Wallington is an exception. It is neither one of Noel Coward's stately homes of England, nor 'a historic house'. Rarer still, it is a historic home. The site, once a defensive pele tower owned by the Fenwicks clan, was transformed into a house, first developed by the Blacketts, shipping, mining and lead magnates, and subsequently through marriage by the Trevelyans, landowners of a somewhat untypical cast. They included poets, politicians, civil servants, historians and patrons of the arts in successive generations.

In the 19th century, a previous baronet had 'thought it wrong for any man to own too much property'. In 1937 Sir Charles Trevelyan announced: 'As a socialist I am not hampered by any sentiment of ownership.'

Transferring the estate to the National Trust, to take effect after his death and with the proviso that members of the family would continue to live in part of the house, he was satisfied that 'the place I love will be held in perpetuity for the people of my country'. Wallington opened to the public in 1968.

For the past 18 months the house has been closed and £1.7m has been invested in restoring it. The roof has been reslated, more than ten miles of insulated cable has been laid, a controlled temperature and humidity system installed and the incessant problems of damp resolved.

Fragile plaster ceilings have been pinioned and restored from above. Some original and unusual colour schemes have replaced the standard grey-green shades of the National Trust. The house is once again expressing a personality, articulating the amiable eccentricities of past generations.

Delight in the perfection of country house style is a new phenomenon. The original owners and visitors were less adulatory. 'Execrable, within, without and almost all round', 'vast rooms, bad taste, much indifferent tapestry', 'built by somebody that is mad', are only a few 18th century epithets. Augustus Hare in the 1860s described Wallington as 'endless suites of huge rooms only partially carpeted and thinly furnished with ugly...furniture'.

'His hostess,' he complained, 'was hardly concerned with her guests' comfort, feeding them solely on artichokes and cauliflowers.' Lady Pauline was at that time consulting John Ruskin and others on roofing over the courtyard and the commissioning of the decorations for the resultant central hall. The poet Swinburne commented that the Wallington air had become 'contaminated with Pre-Raphaelite incense'.

William Bell Scott was commissioned to paint eight large Northumbrian historical scenes, which incorporate portraits of the family, their agents and friends. Lady Pauline stands defiantly on Tynemouth Rock facing ravaging Viking hordes, while the future baronet is shown improbably as a foundryman in the industrial compilation of iron and coal. All of the eight were conserved as part of the restoration project.

Succeeding generations of Trevelyans have contributed their own characteristics. A series of freethinking aristocrats have at various times advocated public access to the countryside, Irish Independence and tariff reform, while arguing for the abolition of the House of Lords and all 'spirituous liquors'.

A touching photograph shows a two-year-old Geoffrey Trevelyan canvassing for his Labour candidate father in the General Election of 1922. His placard reads: 'Vote for my daddy.' I like the sound of Sir George who was a 'hearty Protestant' who 'did not understand Christianity' or the near-sighted Lady Eleanor who trotted round the estate calling 'cuckoo' to attract her baronet husband.

There is so much to see in the house. In the entrance hall is a wonderful collection of Ming and Kangxi porcelain, plus some rare Bow figures and two delightful early English Delft election punchbowls. Portraits abound, some quaintly primitive, others by Gainsborough, Hoppner, Burne-Jones, Reynolds and Romney. Ten panels of exquisite oriental-inspired embroidery made by Julia, Lady Calverley, are themselves alone worth a visit.

The famous collections of doll's houses and model soldiers remain intact. At the very top of the house is Lady Wilson's cabinet of curiosities, a hotchpotch of the strange and the wonderful. Somewhat depleted by gifts to museums and universities, it still boasts stuffed birds, coins, narwhal tusks, fossils, bones, a remarkable porcupine fish, a rare model of the Holy Sepulchre in Jerusalem and a small piece of the deck from the Victory, supposedly where Nelson fell.

Wallington is a quirky, special place, well worth a visit if only to feel what Ruskin called its 'peculiar Northumberlandishness'. This unreformed leveller loves and recommends it highly, but only if you promise to go away afterwards and tell nobody what you have seen.

Peter Lewis is a writer and the former director of the Beamish Museum

Project data

Cost: £1.7m
Funders: Internal, generated by visitor and membership revenue
Architects: Waring and Nett
Contractors: Kier Northern