I am not a lawyer (and this is not legal advice)
But, as I understand it, in normal times, it is the job of the police to enforce the law. Something becomes a law when it is proposed (usually by Government) is voted on in parliament and passes through various stages into statute. We are not in normal times so the government have given the police powers to enforce things that are not (yet) laws. The question is do those things include both government instructions and government advice? I think the answer is yes
Broadly but not quite correct right at a level of detail level Joker - and the detail is always I think really important when measures that curb normal rights and entitlements of citizens are concerned, especially when they are draconian.
The measures most under debate in this thread are the removal of the right to move around outside your home . That has been outlawed except under a handful of defined "reasonable excuses". But that was
not done through the Coronavirus Act 2020 which was scrutinised and passed by both houses of parliament last week.
Instead, it was enacted through secondary legislation, from a public health statute of 1984 which gave the Secretary of State the power to create new laws arbitrarily (in effect) by simply writing a Regulation - in this case the Health Protection (Coronavirus, Restrictions) (England) Regulations 2020 - which don't need parliamentary scrutiny, they just need to be 'laid before parliament'.
The government hasn't, as Joker described it, given the police powers to enforce things that are not yet laws (which it could never do, constitutionally), but it has instead created the laws, without the active scrutiny of parliament, it needs to fine and arrest people who leave home without sanction.
We might say that's essential and proportionate to save lives in the current emergency (I do, and morally I say we should in any case all be following the current advice for as long as is clearly necessary). But history shows that laws created during emergencies have a strong tendency to stay in place long after their sell-by date, and to be used in some cases for purposes for which they were never intended but 're-purposed' by law enforcers.
And unlike the main Coronavirus Act, which lapses after two years, the restrictions on our leaving home imposed under the Regulation have no 'sunset clause' - the Secretary of State (ie the government, the executive) must 'review' them every 21 days, but with no recourse to the legislature.
Some will say why am I banging on about details of legal rights, we all need to be doing the right thing, and people are at risk of dying. But I make no apology for keeping one eye on what our government is doing with our basic civil rights meanwhile. Trust, but verify.