The bungs are on and protecting the ace from car park incidents as we speakI put 5 additional washes on the outside end of the bolt on the near side, and the far side one turned out to be the correct length.
In the light of day I discovered there was a pinch bolt as et_al suggested (pays not to do these things in the dark with only a AAA headtorch?) so I loosened it off and with a bit of extra leverage from a peice of squashed pipe I managed to get it ondone quite quickly.
Thanks for your advice everyone!
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