John Edgar wrote:
You do not need to be humane, but maleficent in the extreme. They are
vermin and will do untold damage in your roof. They may look like
charming rascals, but they are more like monsters.

Put some poison in your roof space. That gets rid of them. You do not
ned the female giving birth up there, because the whole family will
keep coming back and they are extremely persistent. You need to kill
them all quickly. If you do not get rid of them, they will eat through
electric wiring. It all gets very expensive.

It does get expensive. I have recently replaced all the wiring in
a loft in a semi-detached house. It was nibbled bare in many places,
and a flex to a loft light had been gnawed through. The loft
insulation had been tunnelled into, raked about, and was covered in
squirrel excrement and urine. Some joists (2"x4") had been chewed
badly, about 30% of their cross-sectional area having been removed.
The loft hatch had apparently been a favoured spot for urination,
and the white gloss paint had bubbled off along one side. The owner
had previously re-wired and installed new loft insulation after the
same problem.

I've never heard a way to deter them that works. If you can find
out how they're getting in, stop up the way, but you may well find
that disposing of the individual that's found its way in is best
as they are persistent little osds and will try to re-open their
route in.

Try a Fenn trap (Mk IV). Follow the instructions. They're about a
tenner each to buy. You can get them at good fishing/sports shops,
or on the 'Net, eg: http://www.vespestcontrol.co.uk/fenn.html
http://www.euroguns.co.uk/acatalog/Fenn_traps.html Bacon rind tied
around the plate is good bait. Mind your fingers when you set them,
they are a bit vicious (don't put your fingers near a live squirrel,
either!). Make sure you inspect the trap at least twice a day for
humanitarian reasons. Also, make sure you fasten the chain on the
trap down so it can't be dragged away into the eaves. Otherwise, a
"live trap" is useful (use maize for bait) - when you've caught a
squirrel, dunk the trap and contents into a water butt. It's illegal
to release a caught squirrel elsewhere.

You can use poison bait, but you'll only be able to buy rat bait,
and there's so much else for a squirrel to eat in an urban
environment that it's hard to get them to eat it (although they
will eat PVC cable insulation - "go figure").

You could also use an air rifle, and as it's one of the breeding
times for squirrels at the moment, if you see a drey being built,
knock it down with a long pole.

The next-door neighbour in the semi. above bought a "live" trap,
and disposed of one. He also got two with an air rifle, although
they were outside, and may not have been the culprits. I got one
in the loft I re-wired, and the resident there is now much happier
and safer (fire/shock hazard from wires). They were getting in
through a gap in the soffit, climbing straight up the external
corner of the house!