Work depicting aristocrat as a young poet will remain on view at Powis Castle in Wales. One of the finest British miniatures, by Isaac Oliver, has been bought by the National Trust. Valued at £5.2m, it has been acquired for £2.1m, because of tax concessions on a sale to a public collection. Even at the lower figure, it is probably a record price for a British miniature. Depicting Edward Herbert, 1st Baron Herbert of Cherbury, the miniature (around 1610-14) will remain on display at the National Trust-owned Powis Castle, near Welshpool in Wales. The sitter was a poet, philosopher and statesman. He is shown as a fashionable and melancholic young…