I have had a little bit of feedback on the gulls and have done lots of research. Despite posting the pics on birdforum I had nothing back save a solitary vote for Lesser Black-backed Gull for the bird on the deck and this along with some correspondence on twitter was my thought but it didnt sit well. Yesterday Michael Flowers managed a shot of the open wing which showed it to be dark with a small, faint window. Allied with some correspondence on twitter and it became clear that this is a Yellow-legged Gull due to its generally pale appearance, strong bill, underwing marking and leg length. The marked UTC's also point against Caspian.
In reference to the flying bird I have had no feedback but I have studied Olsen & Larsson quite a bit and the relevant features for 1st-winter Caspian Gull are present - the pale underwing with whacking great windows in the primaries plus the generally pale appearance, clean UTCs, tail bar pattern and long, parallel sided bill on a small head.
Im quite chuffed that I managed to get a handle on these bits as I'm not the best at immature gulls - Im constantly befuddled but I kept returning to it and am happy with the results (and chuffed with the outcome). Caspian Gull is a new bird for Yorkshire for me and the Yellow-legged Gull was only my 2nd in county I think.