The Crown Prosecution Service (CPS) have issued guidance on what may be reasonable and lawful, under the Health Protections Regulations 2020 the document document, which was published last Thursday, and applies to England only.
The guidance, which has been published by the College of Policing, to all police forces in England, perhaps in an attempt to ensure its officers to operate within the law? (Don’t hold your breath)
The guidance is broke down into three areas:
The first being tiled NECESSITIES (see below)

This will be helpful to assist the community to determine what they wish to purchase.
If you are out and about on your shopping trip for food, takeout, taking pet to vet, buying It confirms that people can buy “non-essential item# food for a vulnerable person, family member, neighbour, volunteering working and you want to purchase ‘non essential” item it is reasonable and proportionate to do so. The guidance confirms that people can buy “non-essential item. NOTE: The legislation does not set out what a “non essential” item is.)
It appears to question whether purchasing paint is reasonable. What is the difference between repair and maintenance? ( Note this may be open to a legal challenge depending on the circumstances)
The second area titled EXERCISE ( see below)

This may assist the community to advise an ill informed police officer as to your rights.
You can drive to and walk in the country side, on the basis that your walk is for a longer timescale than the time it took you to drive.
Whilst having a long walk, you can stop and have food, this maybe referred to as a picnic.
If you walk local then stop for a “short period” on a bench maybe reasonable. ( Note this is a grey area and may give rise to a legal challenge. Recently police have been keen to over reach their power, whilst purporting to be acting in the interest of the NHS)
The law does not define “essential travel” or say how many times people may exercise outside a day. It does states that: “During the emergency period, no person may leave the place where they are living without reasonable excuse.”
Going to Work…
There is no requirement to be a “key worker”or an “essential worker” to be able to travel to work. Any one can travel to work, if they are unable to work from home or require to collect work. The test under this legislation states, where it is not “reasonably possible to work from home”.
There is no requirement in law to carry a letter or ID as proof you are going to work, this includes volunteering. The police have no power to request sight of any documentation or ID. In short there is no power to “Stop and Account” under this legislation.
The Third. Being Other reasons (See Below)

If you need to leave you home and stay with friend to cool down this is permitted. The guidance suggest the stay maybe measured in days rather than hours.
(NOTE: This test is not in the legislation therefore open to challenge) This guidance arrives from an interpretation allowing people to “move between houses”
Taking you pet for urgent treatment at the VET.
Strong Communities build better lives!
Remember our communities look after each other. Everybody must follow the guidance on SOCIAL DISTANCING or PHYSICAL DISTANCING is a SOCIAL DUTY it will keep us all safe, and keep the police away.
Keep TWO. METERS or SIX FEET apart when you go out.
Source: https://www.college.police.uk/What-we-do/COVID-19/Documents/What-constitutes-a-reasonable-excuse.pdf