TheDoctor said:
Get thee to a dentist, Landers!
Handy hint (passed on by my dentist some while back)
Don't use Araldite to replace a filling. It's a complete sod to drill out.
Boots (other chemists are available) do temporary filling replacement kits.
Ah, the whole sorry story...
Old filling falls out.

NHS direct advise a temporary filling (which works pretty well once it settles in).
After finding dentist, going for initial consultation and returning to get filling fixed, dentist says that the temporary filling is a complete sod to drill out (although the packaging describes it as "easily removed by your dentist").

As a result, the replacement filling is put in on top of the temporary one, which being slightly squidgy doesn't give an entirely solid base.
"We'll see how it goes," says the dentist.

I'll tell you how it goes - the replacement filling lasts two days before cracking and falling out.

Back to the dentist to try again...
Dentist drills out a bit more temporary filling, and tries a different filling compound.
"We'll see how it goes," says the dentist.

And it's lasted all of two months this time...

Perfect timing, given my impending holiday and new job in London!!!