Looks like a body on the line causing disruption to GN - assume there's a fair bit being diverted via Hertford.
http://www.whtimes.co.uk/motoring/g...ld_following_woolmer_green_fatality_1_4581723
http://www.whtimes.co.uk/motoring/g...ld_following_woolmer_green_fatality_1_4581723