Martin Brown wrote:

Actually the mice got very little if any food -
conceivably there were a small number of crumbs on the floor.
I suspect they came in out of the cold.

Figuring out exactly how they got into the room(s) and closing the gaps
off with a stainless steel mesh ought to help.

Chances are there is a rusted through air vent grating somewhere.

I've worked out how they got into the 2 rooms.
In one the cover of an air vent was on the floor -
I'm not sure if the mice pushed it out or if it was not on.
I'm planning on blocking the air vent, so that case should be solved.

In the other room the mice entered through a door onto a balcony.
The catch on the door is broken, and the door was very slightly ajar.
Again I should be able to close this firmly.

The mice or mouse were on the balcony again last night,
as evidenced by a few droppings, and a small pool of mouse pee.

I find Nutella makes excellent mouse bait. The odd one gets inside our
loft from time time time usually in late Autumn. That is by climbing a
vertical wall and finding a small gap somewhere under the eaves.

I'll follow your advice with a couple of traps and a little poison
on the balcony.
Thanks for your suggestions.

--
Timothy Murphy
gayleard /at/ eircom.net
School of Mathematics, Trinity College, Dublin