''The Screaming Scarlet Marquis'' was how Oscar Wilde described one Scottish grandee, his persecutor, Lord Queensbury. The Marquis of Lothian, who has died aged 82, embodied an altogether more pastel shade. A lieutenancy in the Guards from 1943, time in the diplomatic corps, steady, Conservative duty-doing in the House of Lords, loyal service in junior ministerial office, devoted care for the family properties, including the rescue of Ferniehurst Castle, the career of Peter Kerr would entitle him rather to be called ''the discreet, pale blue Marquis''.

The Kerrs of Roxburghshire are old land and old money, the sort of proprietors unlovingly chronicled by Tom Johnston in Our Noble Scots Familes, this one holding lands on the border and in Derbyshire. The Kerrs, or Kers as it was more often spelt (''Carr'' in aristospeak), were a furious presence in the Borders at least as far back as the fourteenth century, ''a leading tribe'' as George MacDonald Fraser put it, ''of the Middle marches''. But they were as remote from the late, gentle, widely liked marquis as very well could be.

Though they were wardens

of the border, no family, says

Fraser, was more active in raiding. The branch from which the Lothians descend includes Dand Ker, who seized Kelso Abbey in 1515, putting the abbot on the road. Anglicised, perfumed and corrupted, they provided the Robert Carr, Earl of Somerset and catamite of James I, who, with his wife, Frances, murdered Sir Thomas Overbury in the great criminal case which shook the crown's credit.

The early Kerrs did sterling work during the Reformation despoiling Church lands, notably Newbattle Abbey, and realising the proceeds. It pro-vided their first title, a barony, in 1591, though they made some amends to the Catholic party by looking after Mary Queen of Scots on her last travels in Scotland. However, in quieter times, their leap to a Marquisate in the early 1700s seems to have been simple politics, probably deriving from the policy of inexpensively squaring the Scottish nobility in the run-up to Union by bumping up their peerages.

Fire and slaughter could not have been further from the private and public life of Peter Kerr the 12th Marquis who inher-

ited the title in 1940. Like more recent holders of the title, he

was a devout Roman Catholic, holder of papal decorations including a knighthood of Malta of which he particularly proud, and he served as trustee of a monastery in Umbria. The Catholic convictions were deep and sincere.

The life he lived was quiet and useful. Born in 1922, he married in 1943 the daughter of another Catholic family, Antonella Newland, whose father, Sir Foster Newland, a distinguished diplomat, may have encouraged young Lothian to enter that service after the war.

He had inherited the title on the death of his father's cousin, the eleventh Marquis, Philip Kerr, ambassador in Washington, a man who had played a controversial part in pre-war politics as a member of the Cliveden set, who aimed to avoid a Second World War by maintaining unofficial contacts with Germany.

His own father, Andrew Kerr, had been a captain in the Royal Navy. Educated at Ampleforth College and Christ Church Oxford, Peter served from 1943 in the Guards regiment.

A variety of diplomatic posts from the end of the war to the mid-1950s culminated in his appointment as a member of the British Delegation to the United Nations General Assembly. Always a ready attender in the Lords when overseas duties permitted, he shifted delicately into politics of a mild sort, first as delegate to the Council of Europe under the Tory label, then as a nominated Conservative member of the Strasbourg parliament of what was then the EEC.

He became, in 1960, the protege of another Lowland magnate, Lord Home, at the start of his three-year stint as foreign secretary. Lothian served as his PPS in the Lords until 1962. The position brought him modestly into foreign affairs in interesting times, the Cuban missile crisis and the visit of Bulganin and Khruschev to London. In 1962, he rose to ministerial office as under-secretary at the Ministry of Health.

He spoke for the Tories in opposition in the Lords and

had another shy at office with two years as under-secretary at

the Foreign Office in Edward Heath's government, where he offered cold comfort to those who hoped for a stronger policy toward the regime in South Africa. Personally kind, he was not a notably imaginative figure in foreign affairs.

As a landowner he was conscientious and rather innova-tive. He opened his handsome English property at Melbourne in Derbyshire in 1952, letting the public into Melbourne Hall for the good old-fashioned price of two shillings (10 pence), undercutting nearby Knowsley which charged half a crown.

More importantly, he bought and set about the restoration of Ferniehurst near Jedburgh. Belonging originally to another set of dangerous Kers, this is a raider's tower with later extensions and any amount of romantic (and bloody) history: built in the fifteenth century, razed by James VI for harbouring Bothwell, rebuilt in the same decade, but latterly much decayed. Lothian fully restored it and would spend some part of the year living there.

His marriage to a lady rather more flamboyant and much engaged in Roman Catholic causes, was a happy one, with six children including his successor, the Earl of Ancram, long familiar as a presence in Conservative governments and shadow cabinets, currently keeping up his father's interests as party spokesman on foreign affairs.

As a very senior nobleman in the kingdom and especially in Scotland, Lothian was heaped with honorific posts: lord warden of the Stanneries, keeper of the privy purse to the duke of Cornwall and commandant of Special Constabulary of the Borders. A good natured, kindly, notably ungrand aristocrat, regarded with warmth and affection, Peter Kerr kept his family's name in quiet, honest credit.

Peter Walter Francis Kerr,

12th Marquis of Lothian;

born September 8, 1922,

died October 11, 2004.