@BillHopkinson wrote:
Thanks for your reply. I ran the test simultaneously and got slightly better results.
Still can't access Sam Knows. Disappointed that Virgin can't / won't help further as the router is getting full speed. I've replaced both ethernet cables, and updated the drivers to the network cards (which are definitely 1gig).

So just to confirm if you run a test on both PCs, at exactly the same time, you get 360Mbps (Or more?) on both?
If they both get 360Mbps at the same time that means you have at least 720Mbps.
This means the issue is somewhere else, rather than your internet connection.
Personally I find most speed test sites to be inconsistent.
Of all of them I find fast.com to be pretty good (I have to set the max 'Parallel Connections' to 30, under 'More Info' / 'Settings', to get the best results):
