A written constitution is in most regards Law set in stone.
No, it's not. Every constitution I've ever heard of has a mechanism for amending it.
Even the American constitution, with the greatest hurdle I know of for amending a country's constitution, has had 12 amendments in the last century.
The Canadian constitution was only repatriated from Britain in 1982, but since then, it's been amended 10 times itself.
British laws can always be over ridden either by parliament or in the supreme court.Or indeed by referendum. Mostly this can be done with a simple majority.
In the case of a referendum this can be set in the bill that sets them in motion.
And how exactly would a single document that spells all this out be an impediment to amending it?
You're talking about the test for amendment, not the form of the constitution. The mere fact that it's all written down in one place doesn't mean it's necessarily harder to change.
Not having a written constitution allows a Government to take actions for which they have a majority.
But is this good or bad?
Your own parliamentary system (and mind) recognizes that sometimes more than a simple majority is necessary when it comes to serious matters of law.
This is why you have a two-chamber system. It's why every bill requires royal assent. The more important the matter, the more it deserves re-examination and careful reflection. A constitution with a significant hurdle for amendment is one way to address this.
Things like
habeas corpus are more important than next year's budget for the Export Credits Guarantee Department. I think it's completely justified that a stricter test needs to be met before one is changed than the other.
We never impose constitutions on former colonies, however they usually ask for one.
and implement it themselves. It can not be imposed.
I don't think you know much about Canadian history, then.
The British North America Act, i.e. the original constitution of Canada, was an act of British parliament. All amendments to the Canadian constitution were passed by the British parliament until 1949, and Canada didn't get full control over its constitution until 1982.
We do not have a hierarchy of laws, new laws must be written in ways that do not conflict with existing laws.
Then you do have a hierarchy: old trumps new.
If an error is made in drafting, it would fall to the supreme court to decide on resolving them.
And what basis do they use for their decision? One law will be struck down and one law will prevail... hence an implicit hierarchy.