Drovers Way / Brewer's Hill Road, Dunstable in particular.
It should be obvious...
When you are moving into a 20mph zone it needs to be obvious. Turning left into Drovers Way from 30mph to 20mph the 20mph sign can easily be missed. Make the road narrower, say 25 yards into Drovers Way, Simple road striping could be used to narrow the road, but also make sure the 20mph signs are next to the narrowing stripes.
"Where a limit starts near to a junction, great care must be taken in siting the signs to ensure that they are clearly visible to turning traffic. Advice on the spacing of repeater signs for 20 mph speed limits is given in Traffic Advisory Leaflet 1/95"
"Previously, 20 mph zones were not permitted if any part of the zone was more than 1km from any boundary road. Although this no longer applies, it remains sound general advice"
"Gateways can incorporate coloured surfaces, with or without a 20 mph elongated roundel marking. Where a 20 mph roundel is used, it is strongly recommended that it is placed on a coloured background to give it prominence. "
To CBC: Download, Read, Digest, and Implement : http://www.20splentyforus.org.uk/UsefulReports/Dft_TAL-09-99.pdf
UPDATE 16 August 2016: I got the information I requested, and posted this report for Dunstable News Desk: http://dunstablenewsdesk.blogspot.co.uk/2016/08/6000speedingtickets.html
UPDATE 15/9/2016 - A second FOI request - reported this on here: http://dunstablenewsdesk.blogspot.co.uk/2016/09/dunstable20mph.html
Further debate generated from this: https://www.streetlife.com/conversation/1f1fjjp8ikxsu/