Crikey - over a year old this reply and I didn't see it!
Yes, it does look like a carved gatepost, but if it's a rough cut rather than properly quarried and worked, it is possible that it could be a recycled stone. I'm closely checking out the gateposts I see on my walks around rural Wirral these days to see how well they have been cut. I need a stonemason's opinion really to help me out.
Something is not right. This message is just to keep things from messing up down the road