Today, I went out to change it. I jacked the car part-way up, removed the nuts, jacked it up further... and discovered that I couldn't get the wheel off.
Then I had a look around. Turns out I have two flat tyres. And all four are pushing the bounds of legality regarding sufficient quality of tread.
So the boys and girls from KwikFit have been called out and they'll be replacing all four sometime tomorrow morning, and charging me nearly £500 (€565, US$725) for doing so.
I have 200 miles to drive before 3pm tomorrow.
In other news, this has prompted me to catch up on all my overdue invoicing.