Can you not just fill every hole/under every floor/outside every wall/all over the attic with the most powerful mouse/rodent poison you can get?
you know the stuff that will leave piles of dead cats outside your house after a few days.
might not get rid of them but might keep the numbers down.
The council already tried that mate, not quite to that extreme but they definitely went to town on it... the boxes and exposed baits are matted with rodent hair, but there isn't so much as a nibble missing from them. ;\
Rentokill made the analogy of dry porridge made with only hot water, to a Sunday roast. Which would you pick? The house is allowing such free access to and from outside that the mice are enjoying fine dining in the garden and the farmer's field, and coming home just to sleep, breed and wreck havoc. The poison isn't even really attracting them aside from, as I said above, the Eradibait which they seem to have confused with wood.
The pest guy says that for every 10 I kill, 20 more are moving in. He spent an hour surveying every nook, cranny and hole inside and out, and said he can clearly see that they are still 'pouring' into the house from outside. Bleurgh.
