It was a long time ago, but as I remember, you need to take the plastic grab rails off (4 x 12mm nuts under grey plastic covers) and then the rear grey plactic cover (10mm nuts found upside down under the rack above the tail lights) and then the black metal one beneath it (this has some hex screws holding it in place I think). One this is off you can get a ring spanner (14mm I think) on the relevant nuts.
It sounds more complicated than it realy is.

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We are now retired....so....... lots of this and this and no more of this or this