YESTERDAY Queen Elizabeth attended a service of Thanksgiving for her 80th birthday at St Paul's Cathedral and tomorrow her official birthday will be marked as usual on Horse Guards Parade when the Welsh Guards will Troop The Colour. Events of this kind are an important part of the “mystique” of the British monarchy and contribute to its lasting success. However, this week another royal event has been taking place in London whose appropriateness must be open to question. At Christie's salesroom the household effects of the late Princess Margaret have been under the hammer in order, we are informed, to raise money to pay inheritance tax on her 7.6 million estate. By all accounts the sale exceeded expectations with most items going for many times the auctioneer's estimates. Three plastic umbrellas with a street value of a few pounds were snapped up for 2'000 pounds because the royal hand had once held them. Extraordinary prices were paid for jewelry and fine art objects, many of them gifts to the Princess and Lord Snowdon from Commonwealth governments when they married in 1960. It is difficult to know which is the more remarkable, the willingness of buyers to pay ludicrously over the odds because of the royal provenance, or the readiness of the Princess's two children to arrange a public sale of the intimate possessions of a woman who always insisted on recognition of the position of privilege she occupied.