It will be up to the police to decide if the allegation amounts to a case of criminal activity. Given that the alleged blackmailer (the Chief Whip) would not make any personal gain from the alleged threat, nor would Wragg seem to suffer any personal loss, I doubt that things are anywhere as near so simple as some here seem to thik.
Definition of blackmail from the CPS website:
The offence of blackmail is committed when a person with a view to gain for themselves or another or intending to cause loss to another makes an unwarranted demand with menaces. (Section 21 of the 1968 Act) Dishonesty is not an element of the offence.
"Gain" and "loss" are defined at section 34(2) of the 1968 Act and are limited to gain or loss of money or other property. The gain or loss may be temporary and include gain by keeping what one already has and loss by not getting what one might otherwise get.
@Florianus, you keep berating other people for supposed ignorance. Do you think it might be worth acquainting yourself with the facts before making assertions like this?