Just found out that it was a transaction made with Great Universal! Not only that but the scammer had tried to do one beforehand for £863.26, I'm thinking this was declined due to lack of funds.
Woke up this morning to an email saying my password had been changed at 2am, logged onto my Halifax internet banking and saw I was £540.48 down. Called Halifax who have confirmed someone has made an online purchase at that amount so have cancelled my card, reset my password, set up an investigation, and will call me tomorrow.
I have never had anything like this happen before, just wondering, has anyone gone through this with Halifax and/or Great Universal and come out unscathed? Thanks.