IS there anyone under 40 who knows who Princess Margaret was? And in any case, do they care?

Yet Princess Margaret, the Queen's younger sister was the Princess Di of her day - beautiful, glamorous and constantly in the public eye.

And capable of charming the most unlikely people. She could be incredibly grand and regal and yet enjoyed nothing more than late night sessions of music and whisky with slightly raffish friends.

Hard to remember that when she married a commoner, Antony Armstrong- Jones, that it was considered incredibly daring.

She also had well publicised affairs, notably with society gardener Roddy Llewellyn and yet produced two apparently well balanced children, successful in their own right and with happy marriages - a bit different from her big sister.

The princess could - and often did - dance till dawn, yet she was also deeply religious with a sincerely held belief.

There were odd spin-offs to this - at a long state banquet in Swaziland she and Kenneth Kaunda, president of Zambia whiled away the boring bits by drawing on their Presbyterian experience and singing metrical psalms together. The way you do She was, of coursed always overshadowed by her sister. Princess Margaret's sense of duty was probably nearly as strong as the Queen's, yet she was always second best - third, fourth and fifth best when her nephews and nieces gradually pushed her down the pecking order. Can you blame her for swanning off to her villa in Mustique?

She became the subject of gossip, some of it spiteful Her last few years were sad and pain-ridden.

Tim Heald's research included all sorts of sources, from Princess Margaret's dutiful thank you letters to her grandmother - "Darling Granny, thank you very much for the lovely bracelet. It was very kind of you to give me such a beautiful present. I had a very nice birthday.

I hope you are well. Lots of love from Margaret" - to the behind-the-scenes planning and preparations for royal visits - "I would prefer anything other than look at a sugar factory" - and interviews with a few people who felt snubbed by the princess and many more who spoke warmly of her loyalty and wit.

At the end of it all, Princess Margaret sounds fascinating - intelligent, if not terribly well educated, witty and occasionally wise, as well as also being incredibly awkward when she wanted to be. Well, what's the point of being a princess otherwise.

In fact, Princess Margaret sounds so fascinating one can only wish one had taken more notice of her when she was alive.