As Bryan said, defiantly a MOT fail. I am seeing more and more spoke broken these days, due to corrosion and a 50 year old part.
You will have to take the tyre off, strip the wheel down and seeing you are at that stage you, may as well fit a set of stainless steel ones. Stainless is not so brittle and give a little flex.
The worst spoke to have is chromed, they seen to break for fun.