Didn't see it myself, but a friend has just told me that when fishing (crabpots) about 4 miles SW of Bolt Head, S. Devon two days ago he saw a Storm Petrel behaving oddly. Then he noticed a Pergegrine chasing it. After a few moments, the Peregrine grabbed the Petrel and flew off towards the coastline. As he was returning home 2 hours later he saw the Peregrine flying out to sea again.
They aren't uncommon in this area of S. Devon and while I have seen them in the harbour, during the winter, trying to catch juvenile gulls, I have never known them hunting so far out to sea or so close to the water surface.
There are quite a few stormies around now and as they follow fishing boats I suppose they make easy prey. I will have to keep my eyes peeled now, but that was probably one of those once in a lifetime sights.