In the memory of both the Master and of the donor's family, Henry Hony gave (not bequeathed) the portrait of his ancestors Mr and Mrs Byam with their daughter to Marlborough College in 1955 believing that it would remain there and, to use the current parlance, be an educational resource. Then, a gentleman's agreement was all that was necessary for the gift.
As for exporting British works of art, each must be considered on its own merits. With 400 Turner oils in the Tate it would be difficult to argue that the nation needs more, but a Gainsborough of this distinction is a different matter. The only similar painting is already in Florida. Few "grand-style" Gainsboroughs are available to the British public and fewer still are ever likely to come on to the market.
The difficulty with a purchase by any British gallery is that it will need the help of the Heritage Lottery Fund which, after the debacle of the Churchill papers, concerns itself with the status of the vendor. And it is unlikely that it will wish to line the coffers of a privileged school. It is a strange contrast with the purchase by the Fitzwilliam Museum 15 years ago - partly with public funds - of a magnificent Poussin owned by the disgraced Anthony Blunt.
One final point. Mr Whittam Smith's skills at editing were much in evidence when he last looked at Gainsborough's painting of The Mall in the Frick Collection. The painting shows at least a dozen women in St James's Park, not three.