Wow thanks to you all for so many useful responses. It seems the consensus is that BA can't be justified at that much of a premium and i would tend to agree. If safety or the perception thereof won't be much of a difference on the two then i can't see how £200 can be justified.

That said, i guess BA aren't likely to get more expensive now as £900 rtn to Vancouver is pretty much top level from my research and experience with booking this sort of flight. The BA price can probably go down whereas the VS will definitely not.

Thanks again, not sure it will be enough to convince my GF but it might help nonetheless.