Litter on side of slip road

Hi, I am reporting litter on this slip road, coming off A243 and onto M25, but there was litter strewn along the motorway all the way from this point to junction 6 where we then turned off the M25 onto the Caterham Bypass. When was this section of the motorway last cleaned? And what is the National Highway Agency doing to prevent littering in the first place. The Department of Transport has written back to me to say measure are taken to warn motorists of littering, but I can not recall ever seeing such messaging, anywhere. A widespread national campaign is needed, on TV and social media, to encourage behaviour change. I was brought up to never be a 'litter bug'. What has happened and why do people now think it's acceptable to dump litter from their cars? Thanks, James