The true answer is no. My wife didnt and wasnt asked for it at UK Immigration. Some here advise yes, just in case, but strictly speaking no. I recall the UKBA website confirms it. Or at least it did back in August / September.
I think one or two folk have been asked for the certification at UK border control, but I believe that they were errors on the part of the Immigration officers concerned.
And now that she is here she hasnt been given a chest xray by her GP as some on the site have mentioned being the case.