Hi Andy,

Thank you for your comment. Having discussed this with the National Trust ranger team in the area, the team were unaware the Icknield way path ran this way which is why it wasn't tagged with horse access. I will go back in and put horse=permissive here now where the route goes through Dunstable Downs. 

Unfortunately I couldn't tell you how the horse route crosses the Tring road further north.

Many thanks,
Jas