I agree about not feeding them, but in your example the "seagulls" are black-headed gulls that don't live only at the coast. They have been breeding inland, by lakes and reservoirs, for many years and competing with other birds in all of that time.
There's no way to get rid of the Lane's feral pigeons without massive expense - and even then probably not. I actually liked watching them on Saturday in the second half - I'm in the Westfield corner - and thought that maybe they were helping to protect our goal.