A quick check of Norwick beach this evening produced a Herring Gull with yellow legs and feet.
Herring Gull at Norwick beach
Interestingly Olsen's Gulls book states 5% of argentatus Gulls in Denmark show yellow legs. This evenings' bird's wingtip with a large white tip to p10 and lacking black to p5 would seem a good fit for argentatus.
