I went to have a look for Japex when I was passing that area the other day, is it anywhere near the speed camera before the tunnel/bridge at all?
Are you thinking about the farm supplies on the right coming from Apsley into kings langley on the back road?
I'm not too sure myself I came off the motorway and then it was second exit off the roundabout at kings Langley , right at the next roundabout and left at the end of the road. I past new flats on my left then speed camera on my right 2-3mins after? Then it said I had arrived on my dodgy iPhone nav!
Thanks for your help