Abstract: The present invention provides compounds of formula (I), wherein R1 represents a C1-4 alkoxy group optionally substituted by one or more fluoro or a C1-4alkyl group optionally substituted by one or more fluoro; n represents 0 or 1; R2 represents a C1-4alkyl group optionally substituted by one or more fluoro or a C1-4alkoxy group optionally substituted by one or more fluoro; m represents 0 or 1; R3 represents H or a C1-4alkyl group; L1 represents an alkylene chain (CH2)r in which r represents 2 or 3 or L1 represents a cyclohexyl group wherein the two nitrogens bearing R3 and R4, respectively, are linked to the cyclohexyl group either via the 1,3 or the 1,4 positions of the cyclohexyl group or L1 represents a cyclopentyl group wherein the two nitrogens bearing R3 and R4, respectively, are linked to the cyclopentyl group via the 1,3 position of the cyclopentyl group and additionally when R5 represents 9,10-methanoanthracen-9(10H)-yl the group -L1-N(R4)— together represents a piperidyl ring which is linked to L2