Publisher:NEL

NEL (New English Library)
A British publisher that is now an imprint of Hodder Headline

Commonly used ISBN prefixes are:
 * 0-283-9 1976–1982
 * 0-340-6 1994–1999
 * 0-340-7 1999–2004
 * 0-340-8 2004
 * 0-450-0 1969–1997
 * 0-450-3 1986–1993
 * 0-450-4 1987–1990
 * 0-450-5 1989–1994
 * 0-450-6 1994–1995

0-340 overlaps with Hodder; 0-283-9 with Sidgwick & Jackson; 0-450 is a pretty clear indication of being NEL though.

NEL also used Souvenir Press and Four Square imprints, but these are likely to be pre-ISBN.

Wikipedia Article

A selection of the NEL and Four Square Horror Covers

SF Master Series
In the Mid 1970s NEL republished several classic novels. The series was edited by Brian Aldiss and Harry Harrison, but introductions were often by another "eminent SF authority". We have these identified so far: