By chance he was in a summer camp on the outbreak of war, and was granted a regular, not wartime, commission in the British Army, in the Scots Guards, later serving in the Guards Tank Brigade, a separate unit from the Guards Armoured Division. He commanded Churchill tanks in Normandy during the Second World War, and in the Battle of Caumont (late July 1944) his was the first Allied unit to encounter German Jagdpanther tank destroyers, being attacked by three out of the twelve of these vehicles which were in Normandy. The battalion second-in-command was killed when his tank was hit in front of Whitelaw's eyes, and Whitelaw succeeded to this position, holding it - with the rank of Major - throughout the advance through Holland into Germany and until the end of the war. He was awarded the Military Cross for his actions at Caumont; a photograph of Field-Marshal Bernard Montgomery pinning the medal to his chest appears in his memoirs. After the end of the War in Europe, Whitelaw's unit was to have taken part in the invasion of Japan, but the Pacific War ended before this could happen. Instead he was posted to Palestine, before leaving the army in 1946 to take care of the family estates which he had inherited on the death of his great uncle.
As Home Secretary, Whitelaw adopted a hard-line approach to law and order. He improved police pay and embarked upon a programme of extensive prison building. His four years in office, however, was generally perceived as a troubled one. His much vaunted "short, sharp shock" policy, whereby convicted young offenders were detained in secure units and subjected to quasi-military discipline won approval from the public but proved expensive to implement and largely ineffectual in stemming burgeoning crime rates. Inner City decay, unemployment and the heavy-handed policing of ethnic minorities (notably the use of the notorious sus law) sparked major riots in London, Liverpool, Bristol and a spate of copy-cat disturbances elsewhere. IRA terrorist outrages on the British mainland escalated, and Whitelaw was personally embarrassed when a mentally ill man breached security at Buckingham Palace and gained access to the Queen's bed chamber.
Two days after the 1983 general election, Whitelaw received a hereditary peerage (the first created for 18 years) in order to become Lord President of the Council and Leader of the House of Lords. In the resulting Penrith and The Border by-election, the Conservative candidate David Maclean narrowly held the seat against a strong challenge from the SDP-Liberal Alliance.
During his period as Deputy Prime Minister and Leader of the Lords, Margaret Thatcher relied on Whitelaw heavily, famously announcing that "every Prime Minister needs a Willie". He chaired the "star chamber" committee that settled the annual disputes between the limited resources made available by Treasury and the spending demands of other government departments. It was Whitelaw who managed to dissuade Thatcher in November 1980 from going to Leeds to take charge of the Yorkshire Ripper inquiry personally.
Whitelaw was usually portrayed on the satirical TV show Spitting Image wearing his dressing gown and pyjamas to cabinet meetings.
Whitelaw privately thought Thatcher should have resigned on the 10th anniversary of becoming Prime Minister. During the 1987 General Election campaign, after listening to a tantrum by Thatcher at a meeting, Whitelaw correctly forecast that "that woman will never fight another election"; she was in fact toppled just over three years later.
Although Whitelaw was given a hereditary peerage, the title became extinct on his death as his daughters were unable to inherit. However, his eldest daughter married and divorced the heir presumptive to the Earl of Swinton, and her two sons by that marriage are in line to inherit that title, so a special remainder to the Viscounty would have seen it submerged in the earldom in any event.
His home for many years was the mansion of Ennim just outside the village of Great Blencow near Penrith, Cumbria. On his death, he was buried at St. Andrew's Parish Church, Dacre.
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