Ark,
You're a constituent in Blaby, are you not? If so your MP is a Lesser-Spotted Blue Representatitve, and you should definitely mail IDS.
After all, did your MP not state that he didn't sign EDMs, since they weren't worthwhile?
You discovered that he does sign EDMs. Therefore, your MP lied to you. Let's not beat about the bush - he lied. Fibbed. Told Porkie Pies, etc, etc.
Now, bearing in mind that IDS's mob were thrown out on their ear in 1997 partly because they had a reputation for being a bunch of lying gits, I'm sure that IDS would be interested to learn that:
a) One of his flock hasn't learned the lesson.
b) That said MP not only lied but sent teddy on an out-of-cot excursion in his reply
c) That said MP's behaviour is more widely known than said MP thinks it is, with an adverse effect on the image of the party. If an MP is prepared to lie to a constituent on the relatively trivial matter of whether or not he signs EDMs how can he be trusted at all?
You ought to name and shame the chap!