found a better way of mounting it if anybody's inerested:
one of these
(presumably this:
http://www.chainreactioncycles.com/Models.aspx?ModelID=32282)
comes with a seat stay mounting bracket, which i've just used a nut and bolt to attach the half of the BLT's own mounting bracket that the light clips to, onto it:
I put some washers in there so that tightening it increases the friction of the bracket onto the clip rather than compressing the shims more (the clip's held onto the seat tube tight enough so that it can't move, but without the washers, the bolt can still just keep squashing the two sides further together). If you notice, the BLT's own mounting bracket has a bolt with a hexagonal head. I knocked this out and used the hexagonal hole for a nut of the same size.
the oxford led can go on the saddle bag:
and used as a backup, or to have on constant with the BLT on flashing or vice versa.
I was reminded of when i once tried to attach a phone holder to the headset top cap using a bolt through a hole drilled in the plastic body- fortunately my phone wasn't in it when it went bouncing down forest town high street. Couldn't get the similarity to that out of my mind... happy now chuffy? !

