(19)

(11)

EP 0 557 335 A1

(12)

(43) Date of publication: 01.09.1993 Bulletin 1993/35 (21) Application number: 91919661.0 (22) Date of filing: 13.11.1991

(51) International Patent Classification (IPC):  G01N 15/ 02( . ) G01N 15/ 14( . ) (86) International application number: PCT/GB1991/001995 (87) International publication number: WO 1992/008965 (29.05.1992 Gazette 1992/12)

(84) Designated Contracting States: AT BE CH DE DK ES FR GB GR IT LI LU NL SE (30) Priority: 13.11.1990 GB 19900024645 (71) Applicant: POWERGEN PLC. London EC2M 1JJ (GB)	(72) Inventors: FOGGO, Stewart Martin Nottinghamshire NG11 0EE (GB) SILLITO, Nicholas Nottinghamshire NG11 0EE (GB) (74) Representative: Harland, Linda Jane  c/o Reddie & Grose 16 Theobalds Road London WC1X 8PL London WC1X 8PL (GB)