There's a reasonable route (two in fact, one about an hour the other around 2-3 hours, with mega mud point) to sprint round from your in-law's place, I've ridden them many times. And whilst sections are muddy (in the Cotswolds it always is) most of it is maintained track. I've got the tracklogs if you're interested – there's nowt around you, other than bridal paths around the flatlands and lakes, not really very inspiring.
There's also some good(ish) stuff out the other side of Naunton, but I only made one worthwhile route there, and I guess there's no point in visiting that part of the world now – tracklog of that available too.
But a trip to Abingdon doesn't take long, and then there's the ridgeway and a good set of routes there – I've not mapped them, but if you're interested I could find a PC to put the SW on and build up the maps.
That mud is the reason I ended up with a winter bike, something with a cheap bottom bracket and other low-spec parts. Of course it never broke…
Andrew