Hi, firstly thanks to all the people who responded, secondly, I still need help!
I have now caught 8 rodents, and one that got away! My problem is still uncertainty. I have always suspected it to be baby rats, my wife thinks mice. Her reasoning was weight related, the quoted figure for weaned rats was 40gm and none of our little 'friends' were that heavy. So I have weighed the recent catches. One (not photographed - one of his siblings had eaten part of his face overnight - yummy!) weighed 30gm. I now attach another photo of two more recently caught. The slightly larger one at the bottom of the photo just looks like a rat to me. It, like the slightly eaten one also weighed 30gm. The top one weighed 20gm! So is it possible we have both rats and mice using the same route into our kitchen (from the void between the ceiling and the floor above, down some boxed-in pipe work) are they the same species, and if rats, very low body weight weaned rats or in the case of two of them, the 30gm ones, heavy mice?