The 'thing' in the loft

There has been something in the loft since we moved here. We now sleep in the main room beneath the loft and you can hear it making noises. It is too big for a rat as it thumps and there is only one of it. It is most active early mornings and late evenings. Most of the time it sounds like it is playing football up there and dust occasionally falls between the brown varnished wooden boards that form the ceiling. My best guess is that it is a stone marten seen below. I have tried to see it by climbing into the loft with a torch but it freezes and I haven't been able to see it yet.

I have found that I get very intimate with wildlife here that you don't see very often in the UK. There are bats in the loft, salamanders in our store and the drains, that emerge when it rains. The birds are numerous and noisy, owls shout most nights and the pair of buzzards fly over every day around 4pm looking for a careless chicken. I have mice in the house and stables and Nosher, my cat has killed at least two rats that I know of and our other cat bought a very live water vole into the kitchen as a gift last summer. Lizards sunbath on the walls of the house, I suspect badgers dig in the soil banks and have made a path across the land. I am grateful that I have not encountered any of the numerous snakes yet. Don't get me started on the wolves in winter, the wild boar etc etc. I really am very lucky to live here.