I am infinitely fortunate to have lived and worked around the lakes all my life.
Take the MTB. The roads round here are perfectly safe, and fantastic to ride.
Unfortunately you are going to have to share them with the most dangerous idiots in the world – tourists!!
I have lost count of the times, I have nearly been killed by someone driving along with their head at 90°, looking out the side window at some sheep. Or a hill. Or whatever else they deem more important than looking where the F$#k they are going.
Besides a MTB can sub in as a road bike better than the road bike on a lake district trail.