(19)

(11)

EP 0 521 032 A1

(12)

(43) Date of publication: 07.01.1993 Bulletin 1993/01 (21) Application number: 91905990.0 (22) Date of filing: 14.03.1991

(51) International Patent Classification (IPC):  E02F 3/ 92( . ) E02F 5/ 10( . ) (86) International application number: PCT/GB1991/000394 (87) International publication number: WO 1991/014834 (03.10.1991 Gazette 1991/23)

(84) Designated Contracting States: AT DE ES FR GB IT NL (30) Priority: 22.03.1990 GB 19900006429 08.08.1990 GB 19900017397 (71) Applicant: BRITISH TELECOMMUNICATIONS public limited company London EC1A 7AJ (GB)	(72) Inventors: SMITH, Trevor, John Fawley, Southampton SO4 1EF (GB) CROAGER, William, Preston Kirbymoorside, York YO6 6BU (GB) (74) Representative: Clarke, Geoffrey Howard  British Telecom Intellectual Property Department 13th Floor, 151 Gower Street London WC1E 6BA London WC1E 6BA (GB)