brimstone
I think that you are probably correct. However, if I were to have an incident while taking off when the reported RVR is below minima then I would start being very very nice to Flying Lawyer. Hence my own personal view on the matter.
Tandemrotor
Have just dug out my old copy of BA FCOs (yes, I know that I should have handed them in!). FCO 725 states that take-off is not permitted if either the RVR as assessed by the captain or the reported TDZ RVR is below minima. However it later states that pilot assessment always overides the reported RVR. That last statement tends to support brimstones view. However, the first statement particularly the word 'either' tends to support my view. I think that even Flying Lawyer might have a problem with this one.
Airclues