I've just found http://www.highways.gov.uk/news/pressrelease.aspx?press
releaseid=425156

Construction of an M25 managed motorway scheme for junctions 5
(Sevenoaks) and 7 (M23) is proposed to start in 2013/14.

The press release says it will be the "first M25 'managed motorway'".
I don't know why the scheme between M3 & M4 does not qualify already.

"The hard shoulder will be converted to a traffic lane to add extra
capacity. Variable mandatory speed limits, displayed on overhead and
verge-mounted signs will help smooth the flow of traffic and reduce
congestion on this busy section of motorway."

The M25 often seizes in the AM peak between J5 & Clacket Lane Services.
--
Walter Briscoe