I looked the at What Car target price and went through Carwow for quotes, most offered around 4.9% off the list price but one offered 8.8%, I went to my local dealer to ask if they could match it but they advised not, "they'd be making a loss". It was then that I noticed that they have the scrappage deals (new for manual diesels only) where you get 4K off the new price, trading in my old Mazda 3 on a 55 plate that I was being offered between £250-500 for depending on the type of dealer/supermarket. I haggled with them an in addition to the scrappage got all the normal stuff, mats, boot liner, tank of fuel and Apple Car Play thrown in too.
If you do go through Carwow it's also worth signing up to Top Cashback or Quidco as they offer up to £100 back too from that, I'm not tight honest!