I think the guidelines are quite simple......Only travel if essential.
If you think driving 20 mins to do a walk, is essential travel, not matter how long or short the walk is then that is your decision but please do not complain if the lock down is extended and/or tighter restrictions enforced.
What if you were to have a car accident on your so called "essential" drive. I don't think the ambulance staff will be too happy to come out to you and I know A&E staff would not be amused. You could be taking up an urgent bed, using vital NHS supples and taking staff away from people who need our doctors and nurses the most during these times.
It's not just about you as an individual getting your daily exercise, this is about the country uniting together. Please think about others and the consequences you may cause.
We are all in this together so why can't we all fight this together.