Gainsborough and Horncastle is a former county constituency represented in the House of Commons of the Parliament of the United Kingdom. It elected one Member of Parliament (MP) by the first past the post system of election. It existed from 1983 to 1997. The area of and around Horncastle is now in the constituency of Louth and Horncastle.

For elections prior to 1983, and from 1997, see Gainsborough.

The District of West Lindsey, and the District of East Lindsey wards of Binbrook, Donington on Bain, Horncastle, Roughton, Woodhall Spa, and Wragby.

Year		Member	Party
	1983	Edward Leigh	Conservative
	1997	constituency abolished

General election 1983: Gainsborough and Horncastle

Party		Candidate	Votes	%	±%
	Conservative	Edward Leigh	25,625	50.9	+3.1
	Liberal	Andrew Phillips	20,558	40.8
	Labour	Carl James	3,886	7.7
Majority			5,067	10.1
Turnout			50,069	75.0
	Conservative win (new seat)

General election 1987: Gainsborough and Horncastle

Party		Candidate	Votes	%	±%
	Conservative	Edward Leigh	28,621	53.3	+2.4
	Liberal	David Grace	18,898	35.2	−5.6
	Labour	Robin Naylor	6,156	11.4	+3.7
Majority			9,723	18.1	+8.0
Turnout			53,675	76.9	+1.9
	Conservative hold		Swing

General election 1992: Gainsborough and Horncastle

Party		Candidate	Votes	%	±%
	Conservative	Edward Leigh	31,444	54.0	+0.7
	Liberal Democrats	Neil Taylor	15,199	26.1	−9.1
	Labour	Fiona Jones	11,619	20.0	+8.6
Majority			16,245	27.9	+9.8
Turnout			58,262
	Conservative hold		Swing

• Craig, F. W. S. (1983) [1969]. British parliamentary election results 1918-1949 (3rd ed.). Chichester: Parliamentary Research Services. ISBN 0-900178-06-X.
• Leigh Rayment's Historical List of MPs – Constituencies beginning with "G" (part 1)

53°21′N 0°30′W / 53.35°N 0.50°W / 53.35; -0.50