Seagull ready for the off

The well-known yodelling call of the gull conjures up pictures of the seaside perhaps more than any other sound. However often they can fly quite far inland in the search of humans' surplus food. They have a bad reputation as being quite aggressive towards picnickers. I captured this solitary gull in the act of taking off from a railing bordering the Clyde Estuary. I'm unsure whether this is a common gull or a herring gull.