I don't know how it works over the Channel to be honest as we don't have 8.33kHz spacing in the UK yet as you know. I suppose though that the same aircraft use the UK 25kHz spaced frequencies that use the 8.33kHz spaced ones so I would presume that the tolerance on the new 8.33kHz airborne equipment has been made much much smaller. Either that or offsetting is not used - which is a distinct possibility.
If I can dig out my original documentation on the subject later on I will do so and post a more enlightened comment but my short answer is : I don't know
