Compounds of the general formula ##STR16## or physiologically acceptable salts thereof, in which R1 is a halogen atom or a group NR2 R3 ;R2 and R3, which may be the same or different, are hydrogen or (C1 -C6) straight or branched chain alkyl; or R2 may be hydrogen and R3 may be group R4 CO or R4 SO2 where R4 is hydrogen or alkyl (C1-4); R5 is hydrogen or one or more halogen atoms or hydroxy or alk