Huwdiprose
Yeah I gave it a go on graphhopper, at the time, just checked again: https://graphhopper.com/maps/?point=51.910219%2C-0.467112&point=51.910818%2C-0.466468&locale=en-gb&vehicle=car&weighting=fastest&elevation=true&turn_costs=true&use_miles=false&layer=Omniscale

I missed making that last part of Sundon Park Road tertiary, which I think may be the ground truth mistake that's giving many of these apps more difficulty than with other roads. I suspect they are given the idea to avoid minor or unclassified roads and stick to larger ones...

I'll fix that now.

Also yeah totally right about the tunnel, that's my mistake, I've gone back to the bridge / tunnel docs and taken another look. You're right! Thanks for pointing it out.