Cheers Andrew, as I said I thought it unlikely both in terms of their normal distribution, and the time of the year, but so far, having listened to calls by other rails, and many recordings of corncrakes, I am left knowing exactly what I heard, and corncrake calls are still the best match, and a very good match at that.
Re time of year though, I am more knowledgable re. wild plants than birds, and I see evidence of disruption to the season ... a few plants which had finished flowering in August ( or should have ) had flowers ... it has been an unusual summer, so I wonder if that could possibly have an effect.
I will look into the birds mentioned by yourself and have a listen to their calls. You asked for more info re location.
I was walking east along the path to the north of the fenced off area. about 50 to 100 yards east of the fenced off area I heard what struck me as the far off sound of someone sawing wood. This came from the left, somewhere in a large area of grassland on the north side of the hill. I looked to see if someone was perhaps pruning trees, but at the same time began to think it was not actually the sound of a saw on wood. there were breaks in the 'sawing' and I suppose the sound was a bit like the repeated drawing back and forth of a wood saw. Anyway, seeing nothing, I walked on until, to my right, i heard a similar sound, but more defined as a 'double syllable' rasping and closer together in time... a little like the classic frog sound from the movies, but harsher and deeper. it seemed quite close, and coming from a small clearing surrounded by gorse and broom. There was a ditch between myself and the area. I listened and tried to define where the sound was coming from, but realised I was unlikely to see anything as it could so easily be coming from in, or under the bushes.
At one point I could hear both the 'sawing' sound to the north, and the fuller grating sound close by. I made my way over the ditch, and the sound stopped. I stayed still for quite a long time ... possibly around ten minutes, and then heard the sound again. However I took a couple of steps towards the clearing, and heard the sound no more.
I was all set to go back to the hill today prepared to record with my phone if i heard it again, but not in this weather