705 consistent parliamentary constituencies projected onto the electoral triangles of ten elections (with Northern Ireland shown separately in later years), shaded by the level of turnout — software by author on an Archimedes computer.
The pattern of turnout can be seen to be clearly related to how marginal a seat is. In the 1950s and 60s a white streak cuts vertically through the mass of constituencies on the Conservative/Labour boundary. In 1970 the safest Conservatives and Labour seats also had a high turnout. During the 1970s the composition is seen to change, and the pattern of turnout alters to reflect this swing. By the 1980s most seats with low abstention rates are held by the Conservative party — but not particularly firmly — being fought on two fronts.