Far from saying that there is a scale of rape, with date rape at the bottom, he said some date rapes are indeed just as 'serious' - meaning date rape can and often is violent and should be treated in the same way as a random park rape (or as Clarke unfortunately put it, a 'proper, serious rape').
Clarke continually tried to stop the presenter from reducing his policy to a tabloid headline, but everyone is doing quite a good job of reducing the interview in the same way. Clarke never said it was less serious if you know your attacker, or if it was a date rape, or any other type of rape. He tried to stop Victoria Derbyshire from using the average sentencing figures (she suggested 5 years) because he said they included figures for statutory rape, which could include consensual sex between an 18 and a 15 year old - legally rape of course because we need to protect people under the age of consent, but anyone who wants to argue that this is the same as a violent rape is just plain foolish. Yes it is still rape and therefore subject to the same law and sentencing regime ('rape is rape is rape' as the presenter put it), but the fact that Victoria Derbyshire read out the judges sentencing guidelines which differentiate between the different circumstances within the crime of rape, shows exactly what Ken Clarke was attempting - rather poorly - to explain.
What a pity he was unable to articulate it better - particularly poor, coming from a Justice Secretary. And what a pity left wing BBC presenters are allowed to cynically manipulate poor expression to sensationalise and sex-up their own