I doubt they'll ever be able to say with certainty that it originated here. I'm just going by the reports that it was discovered in London and Kent, a few month back and started to increase rapidly. It still wasn't showing up in other areas of the UK until a few later and was highly concentrated in Kent. I also agree with you, though. It might not have started there as it would just take one person to take it into the area and then it's off.
It will be in every country now and probably has been for a little while. What these countries are doing by trying to isolate us is probably all for nothing as it will already be on their soil and spreading through the populations.