Sorry but your DH is being a total twat over this.
You've offered lots of compromise names - he's offered none.
This is totally stressing you out, but he seems to find it mostly amusing -
'So, women of the jury, I put it to you that actually, his only objection to Verity is Just Because and when I did my and said right, that's it, pissed off now, had enough of this, Verity it is, he laughed and said ok. Does that sound to you like someone with a real problem with the name?'
-No, it doesn't, it sounds like someone who is enjoying winding you up. 
I'd have had enough by now if I were you, and I'd be telling him that the above conversation and especially his little giggle over the issue of him disliking the name Verity had pushed this into serious territory, and that I took him at his word the other day, and Verity it is.
Oh and I can't help thinking that the reason he is able to assert that he is Not Backing Down is because experience has told him that if he throws his weight around, you'll give in. (With that in mind, his little giggly play-about with the idea of Verity the other day seems even more nasty - 'Oh, I'm going to play cat and mouse with her for a bit, but no worries - when it comes down to it I'll have my way'.)
So don't back down, this time. Tell him you don't want Madeleine. That's it.