Sir Nicholas Cosmo Bonsor, 4th Baronet, DL (9 December 1942 – 21 March 2023) was a British Conservative politician.

Bonsor was educated at Eton College and Keble College, Oxford.

Having unsuccessfully fought Newcastle-under-Lyme in both February and October 1974 elections, Bonsor was Member of Parliament for Nantwich from 1979 to 1983, then for Upminster from 1983 until he lost the seat to Labour's Keith Darvill in 1997. He was Minister of State for Foreign Affairs from 1995 to 1997 and practised as a barrister in London.

In 1994, just before he became a minister, Bonsor had challenged the incumbent Sir Marcus Fox for the chairmanship of the influential 1922 Committee, and narrowly lost by 129 votes to 116.^[1] Bonsor, a Eurosceptic, had previously rebelled against the government by voting several times against the ratification of the Maastricht Treaty in the 1992-93 parliamentary session.^[2]

Bonsor lived at Liscombe Park near Soulbury in Buckinghamshire and was a Deputy Lieutenant of Buckinghamshire.

Bonsor pledged support, by appearing together in a public meeting, to Nigel Farage MEP in his 2010 general election campaign for the Buckingham constituency, standing against the speaker of the House (standing for re-election), John Bercow.

Bonsor was a vice-president of the Standing Council of the Baronetage.^[3]

Sir Nicholas Bonsor was the elder son of Sir Bryan Bonsor (1916–1977) and his wife Elizabeth Hambro (1920–1995). In 1969, he married Hon. Nadine Marisa Lampson, now the Hon. Lady Bonsor, a daughter of Graham Curtis Lampson, 2nd Baron Killearn. They had five children, including Sir Alexander Cosmo Walrond Bonsor (b. 1976) and entrepreneur Mary Bonsor (b. 1987).

Bonsor died on 21 March 2023, at the age of 80.^[4] His eldest son Alexander succeeded to the baronetcy as the 5th Baronet.