Had a weird one today per the title and looking for advice and opinions.
Went to the shops and double locked the car as I always do.
Came back to the car and pressed the driver's door button - nada zip zero zilch other than a faint click/whirr from the rear of the car.
Tried the fob instead - same result.
Tried the passenger door - ditto.
Tried the driver's door again and no change.
Went around to the passenger door again and it was open (or at least the handle had now popped out).
Climbed in and reached across to the driver's door unlock button - zilch.
Tried the driver's door interior handle - zilch.
Pulled the emergency key out of the fob stuck it in the lock and twisted it until I got the tell-tale clunk and hey presto, the driver's door now opened. But it was a right royal PITA to get the key back out.
Despite both doors now being unlocked both mirrors were still fully folded in.
Got in, car started perfectly normally, and unfolded the mirrors using the "press both mirror buttons at the same time" method.
Got home, stuck the car on the battery trickle charge/maintainer and let it go right through to "maintain".
Then tried locking and unlocking the driver's door several times, worked every time without a hitch.
First time I have ever had a door lock problem.
I don't think it is a flat battery or a flat fob battery (renewed about two years ago), methinks it's a faulty driver's door lock module.
What say you?
In the meantime I will grab my spare fob and stick a fresh battery in it.

 

Check your battery connections and the connection where the ground cable bolts to the floor of the boot. (Remove and clean)
However, as you surmise, likely the lock module.

 

The only time I have trouble opening the driver's door is when the temps are very low and everything freezes to everything else. I guess that's not your issue!

 

It sounds like you offended your car and it’s on strike.

 

Oh come on, the British car industry hasn't done strikes for ages!

 

Two chances of that being the cause!
I haven't touched the battery or earth connections for many years so no way any of them have come loose.

 

But may have corroded?

 

Ok ok, enough already!
I went out to the car and checked the battery terminal connections and the earth connection, all were corrosion free and tight as a fish's wotsit.
And the lock / unlock system is working perfectly.
Maybe it was just a random unexplained glitch, maybe it is a sign the door lock module is on the way out, time will tell.

 

+1. Even though they didn’t in this case.