Well, basically, it is not a slam-dunk win, I'm afraid, reason being you approached the restriction signs head-on, rather than from a left or right turn. In addition, there is an advance sign. The only thing is the amount of information on the advance sign and also on the actual restriction signs. Too much to read and digest whilst driving a car, but you have to convince an adjudicator of this, and he'll probably think, if it's 20 mph, one has time to read the Times newspaper !