If he says he is ex-SAS then I for one believe him. After all, who in their right mind would lie about such a thing.
If his claim is inaccurate, he won't be the first one. Anyone remember the case of Roger Day, who turned up at the Armistice Day march in Bedworth a couple of years ago with a fabulous collection of un-earned medals? Including I think, several which would have required him to be both of advanced age (which he clearly wasn't) and capable of being in several places and regiments at the same time. One of which would appear to be the SAS.