Been a very serious RTC between junction 4-5, queues down to the M25, think it might be closed for a while, all the roads around Wycombe are clogging up and the A404 is back past Marlow already.
Was about a mile before J5 when I came south there was a destroyed Corsa (I think) between lanes 2 & 3 and a Transit on the hard shoulder on its side with the whole back end missing, looking as positions and the damage looks possibly the Tranny was on the HS when hit.