It is worth remembering that these are Police issued guidelines - on how police officers should deal with people - they are not the law (as written into legislation by parliament - e.g.: The Health Protection (Coronavirus, Restrictions) (England) Regulations 2020 - (26th March 2020) section 6 of which is on restriction of movement...
the above is the law - and these police guidelines are simply how one group of people chooses to interpret that law - as we have seen - sometimes interpretation is as much about how someone wants it to be as what the law actually says!
the section on exercise simply states:
(b)to take exercise either alone or with other members of their household;
so there never has been a restriction on where / how exercise is taken - if you want to go to the Highlands to yomp a few hillocks, that is legal (might not be sensible - but it is legal!)
interestingly - the bit on shopping is: to obtain basic necessities, including food and medical supplies - which technically cuts out the purchase of anything which is not a basic necessity - i.e. champagne / gin / chocolate / etc. 
so - enjoy life sensibly - if you can ask yourself:
- am I exposing more people than necessary to contact
- am I potentially spreading the virus more than necessary
- could I avoid what I am doing
then perhaps don't - but doing things where you are on your own and not affecting other people - crack on - life has to continue alongside the virus, not be subsumed by it!