Too Northerly

With the strong winds continuing to blow today I headed down to Rossall Point at 13:55 in the hope that I might be able to connect with a Storm Petrel. A few Manx Shearwaters were heading south in the distance, just visible as they arced above the waves before disappearing for a while before reappearing much further along on the horizon. The Isle of Man to Heysham ferry was coming into the bay just after I set up so I followed it on the way in to see if any species were feeding around the back of it or just using it's slipstream to get an easier ride into the bay. After a few minutes I picked up a small dark bird wheeling around the back of the boat however it quickly dropped below the level of the waves and out of sight. It did this 4 times in the next 5 minutes and I noted:
- small size, difficult to judge due to distance but wingspan slightly longer than a small wader such as a Ringed Plover
- all dark body and wings and on one of the sightings I saw a white area/band across the rump
- gliding flight but only seen above the waves on 4 occasions so that may explain this
Any ideas? Storm Petrel was the closest I could come however having only a brief sighting to go on a few years ago I haven't got much experience or what other species it could be.
Unfortunately the wind was too northerly so the birds tailed off further into the watch, so the full total between 13:55-15:45 were:
possible Storm petrel
21 Manx Shearwater south
3 Sandwich Tern north
1 2cy Gannet south close in giving great views
2 Common Scoters
8 Dunlin south
4 Oystercatchers east
1 Ringed Plover south