That whole jesus thing is a load of tosh

Actually the word in Isaiah ("almah") that is usually translated as "virgin" by Christians means "young woman"Hebrew has a word "bethulah" which usually does mean "virgin".Aside from Jewish polemic suggesting that Mary was impregnated by a Roman soldier named Pantherus (or something similar) I think it far more likely that the "Virgin Birth" is a legendary addition to the story.

Only the Gospels of Matthew and Luke have the Virgin Birth story. Luke, we may be reasonably sure was not one of the original disciples. The author of Matthew we don't know much about - but it is most likely that he, too, was not a disciple.Matthew links Jesus' birth with Iasaih 7:14, which as you have correctly pointed out refers to a situation centuries in the past. Luke does not. On the basis of Luke's reference it seems likely that the story was fairly well established in the Christian community at the time of writing (perhaps around 80 AD).