Nancy, By Adrian Fort. Jonathan Cape £25

Viscountess Astor (1879-1964) resembled Stephen Leacock's Sir Ronald, who "leapt on his horse and rode madly off in all directions". The first woman elected to Parliament who took up her seat (in 1919), she was a doer of good when it came to the protection of poor children and, at the moderate end of her war against drink, promoted essential legislation limiting hours of sale. Yet she would see Nazi re-occupation of the Rhineland in the spirit of her friend, Lord Lothian, as "the Germans re-entering their own garden".

She was a good, if bossily good, MP. There was plenty of sense in Nancy Astor, but her life marked the defeat of that sense by prejudice, bad judgment and velocity.

She was good about poor children because, as a Plymouth MP, she went into the slums and saw them – sewn into their clothes for the winter with wads of cotton wool underneath. She also got Mrs Simpson right: "an arch-adventuress of the worst type". Rather more importantly, she got Hitler wrong, partly because she hated France: "one vast brothel". Married to a decent press owner, Viscount Waldorf, she enjoyed from her Palladian house at Cliveden a heavy-gun command of "Society". Seeking with wonderful presumption to maintain peace in Europe, she brought Hitler's ambassador there often. The Astor press – The Times and The Observer – sustained the owner's wife's line until March 1939, when Waldorf faced the evidence.

Sadly, Adrian Fort's biography suffers from a similar mistaken self-confidence. He tries to minimise the calamity by rebutting charges that Lady Astor was fascist herself. She wasn't a Nazi sympathiser, though she had a tendency to lump in the Jews with the French as somehow part of the problem. The point was that with all her virtues, Nancy was an amateur; worse, a self-assured amateur.

She would work hard during the war in bombed Plymouth, open Cliveden to the wounded, keep the love of Waldorf and the friendship of Bernard Shaw. Yet the attempt to promote collaboration with Hitler all through the race laws and early annexations does linger rather.