Perhaps the councillors and Highways England should take a trip to Bath and have a look at the Two tunnels Circuit:
https://www.sustrans.org.uk/find-a-route-on-the-national-cycle-network/bath-two-tunnels-circuit/
And in particular the Combe Down Tunnel:
"The Combe Down Tunnel, at an impressive 1,672 metres, is just over one mile and is the UK's longest cycling and walking tunnel. Travelling through the Combe Down Tunnel for the first time is an incredible experience, heightened by the extraordinary audio-visual installation, ‘Passage’ by United Visual Artists. A Portrait Bench sits at the entrance of the Devonshire Tunnel. "
I have been through it several times and it really is a lovely tunnel, filled with music. I would imagine the Tea Shop and Pub on the route do a great trade from the number of people walking and cycling the route. It would be so short-sighted if the B-H Tunnel was blocked up.
Apologies if this has already been mentioned, it is quite a while since I started reading this thread and didn't want to wade through it all again.