Because pneumatic or mechanical delay switches with outdoor fitting kits
are extortionately expensive, I was wondering if anyone had a good
circuit for making my own...

Ideally a single button press should start a delay timer that activates a
light for a few minutes (to light the way from the garage to the house).

I'm happy enough with digital electronics but my analogue is weak.. it
seems like there should be a way to use mains only for this, with a triac
or SCR to switch the load (1000W) and maybe some sort of rectified feed
to a CR circuit to do the timing. But I'm sure there must be a better
way...

The issue of it being outdoors (basically replacing a dead pneumatic
supposed-to-be-weatherproof switch) is also a problem, but making a
sealed rainproof box with a suitably rated momentary switch shouldn't be
too difficult.

Any ideas?

(I've seen motorised timers in an earlier thread but they were 110V
and in the US - I'm in the UK on 240V 50Hz).