The magic of the place wasn't lost on one recent visitor, a professional photographer who arrived on a job and liked it so much that he offered to lend them his family's collection of old masters. A rather unusual proposition, from which the curator expected the worst but, to his happy astonishment, gained seven early Renaissance paintings from the collection of Sir Thomas Barlow. They were last seen in public in 1957 and last week were unveiled at Kenwood, where they will remain for at least the next five years.
All seven have been hung together in a small dimly lit room, the surface of the pictures glinting like jewels in the dark. Some, like Jan Mostaert's fantastic Portrait of a Moor and Hans Memling's Portrait of a Man in Black Cap have firm attributions, others are a little less secure. One of the most striking of the new arrivals is a little picture attributed to the 15th-century Dutchman Dirk Bouts: a Madonna and Child sitting in a hedged garden in front of an amazing hanging, the gold and creases in the cloth painted with equal brilliance. Behind that the landscape stretches away, painted in layers of thin glaze, a subtle and sophisticated evocation of distance.
I'm not quite so enthusiastic about the Botticelli Madonna and Child, bought by Barlow in 1954 and supposedly the centre-piece of his collection. It has its supporters in the rarefied world of Renaissance scholarship, and its detractors, and others who have suggested that only parts of it are by the hand of the master. I'm not sure one way or the other, but it seems a bit odd, hard-edged and not entirely pleasing.
I'm also not completely sure about another of the new loans that were unveiled at Kenwood last week: a portrait by Alan Ramsay, from another private collection (one of four to have lent new pictures to the house). It's a handsome painting with a nice link to Kenwood (in that Ramsay eloped with the niece of the first Earl of Mansfield, for whom the house was built), but there are a few things about it that don't add up. Ramsay was an extraordinarily gifted painter who could breathe paint on to canvas in thin veils but here and there it doesn't feel quite right: the right hand is clumsy and the lace cuffs don't seem to have his delicate touch. It might just have been an off-day, but the subject is also a bit of a mystery. It was once thought to depict the political economist Adam Smith, but is now generally agreed to look nothing like him. The painting has all the hallmarks of a commissioned work, yet there are odd details, such as an unbuttoned waistcoat, the subject's considerable bulk escaping his clothes - not the sort of thing that a man of substance would tolerate in his portrait.
There are 15 new loans in all, including a good group of 17th-century Dutch pictures to complement the existing strengths of the collection. Nothing among them quite matches the standard set by Vermeer's Guitar Player or Rembrandt's late great Self Portrait, most nominated of all the pictures in the Independent on Sunday's survey, but the house feels fuller than it has for years. Go see.
Kenwood House, Hampstead Lane, London NW3 (0181-348 1286)