Yes, it is wrong for those in the know to us insider knowledge to place bets on anything not open to the public. It matters not the subject nor the institution / business involved, it is illegal and they should be punished - by the law.
Such is the case with the bets on the GE date.
Those involved should be punished and the bookies have all the information needed to identify who made the bets, where and when. Some of them will be associates of MPs and government / opposition officers. Many will have never placed a bet in their lives before now. All will be easy to find so go get them, throw the book....
However, the media is making a huge mountain out of a molehill when it comes to the effect these bets will have on the GE. It will be minimal, if that.