It would appear that my bank blocks overseas transactions as a form of security. I will speak to them tomorrow and ask nicely if they'll permit me to make a transaction to the UK from Canada.
Yes, banks are tightening up on overseas transactions. My bank is doing the exact same thing for overseas purchases from companies I have not purchased from before.
Unfortunately the greatly increased prevalence of online scams is forcing banks to be more cautious.
You just need to assure them that, yes, you
are
the account owner and you
do
want to make the purchase.