I imagine many Tory MPs wouldn’t be happy about it either. It’s a big, black and white target though and will gain international attention. It would be very embarrassing to climb down from it (though there would very likely be a different PM in office by then).
As above they probably don't have to worry about actually hitting it and/or hope it will have been forgotten by then and if not massage the circumstances with some BS figures/regulations. It is what the Conservatives do. Meanwhile it is a nice soundbite for them.