thefinegunmaker - I agree, this might well be a case of "badge engineering" - the English gun trade was notorious for it - and it still goes on today as you have observed!

But, in this case, I suspect that the action is in fact Belgian made as were it seems many of the British retailed Farquharsons, except, of course George Gibbs, who made his own actions. It is quite common to find Gibb's rifles, usually in original black powder chamberings that have been rebarreled for nitro cartridges by other makers.

Normal practice in the English gun trade was for the new barrel to be signed by whoever fitted it. Close examination of the Gastinne Renette would elucidate this.