Right so before everyone jumps to conclusions - what exactly did you find under the floorboards? You've posted the title and then nothing. Don't leave us hanging.
I've been doing ghost hunts around Suffolk for about 15 years and scratching inside walls is almost always something mundane first. Mice, rats, birds getting into the cavity, even pipes contracting at night. I know that's not what people want to hear but its the truth and I'd rather say it than have someone spiral into a panic over a dead starling.
That said, the "weeks" part is interesting. Most animal infestations get louder or you start smelling something. If the scratching stayed consistent and then just stopped dead before you found whatever this is - that's worth talking about.
Post what you found. Photos if you have them. And tell us things like what time of night the scratching happened, whether it was rhythmic or random, and if anything else odd was going on in the house at the same time. Context matters a lot with these things.