*fun update*
I've properly lost it this time, and have cancelled my cards and expect a shedload of post next week! Turns out the Barclays app has an option in it to cancel bank cards, so I used that instead of negotiating with a call centre in India. It asked me quite a few details about where I lost it for some reason, like location and time, which I filled in according with where I think it went astray. Need to get a replacement card from the DVLA but it appears they require £20, which I obviously cannot provide as my card is blocked.
I expect to find it all by the end of the day.