By far a better idea would have been to open up fully in summer when the natural reproduction rate of the virus is attenuated and let it spread at a controlled rate and at a time when hospital capacities are at minimal level.

Glad to read this as this was my gut instinct back when they started to talk about tiers. I'm not going to claim any kind of knowledge in this area but common sense seemed to suggest that delaying (which is all restrictions do) into the peak season for respiratory problems was a bad idea.

Well all a lockdown does is guarantee another lockdown is needed. As modelled by SAGE, IC and so on.

So once you've done one, you've created a worse situation after it so will need another.
Which will make the situation worse so another..and another.

Well all a lockdown does is guarantee another lockdown is needed. As modelled by SAGE, IC and so on.

I'm surprised they have not figured out that once all the money has gone and our credit history blows any chance of a further loan, the priority will shift to food supply. In those circumstances there will be absolutely nothing left for science and other nice-to-haves. You'd think they'd be worried about their own research budgets above their concern for the health and safety of the general public at large.
On the other hand, Britain has weathered bad storms before, perhaps they just hope we can just weather this one as well:

I actually ended up in a conversation about this with someone, saying that we needed a longer and harder lockdown in England that went across December too.

I mean, that's what we ended up with, so I suppose he's happy, but the data also got me thinking: If the November lockdown worked, shouldn't its results be unique to countries that did much the same thing?

Let's take a look at Europe, so that climate is (sort of) similar.

France:

France locked down just before us. Their lockdown must have worked!

What about Spain?

Nice flattening the curve eh! Must have been a hard lockdown.

Not quite https://www.dailyrecord.co.uk/news/scottish-news/spain-declares-new-restrictions-last-22904447

In their situation, a curfew, and tiering seems to have worked.

How about Iceland?

No lockdown 1, let alone lockdown 2. Must have been their hard lockdown!

Finland displays a similar jump (no lockdown 2), Switzerland same again,

Slovenia had a partial lockdown and has had no flattening of the curve for doing so.

Denmark entered a second lockdown a couple of days ago, with shops closing on the 17th, but it would appear that infections were falling around then too.

I would include curves for these countries, but there's a 3 file limit on posts.

It seems like some sort of restrictions are tied with bringing cases down, but not always; there are exceptions to the rule.

Sorry to break this: but lockdowns work to delay disease progress!

Conclusion, the national lockdown from 5 November appears to have caused an immediate fast slump in new cases starting on 5th Nov and continuing until lockdown was released . . .

I'm glad to inform (with some sadness) lockdown sceptics, that it is almost certain that in these circumstances the lockdown worked.

Unfortunately, the conclusion you draw is incorrect. The problem is that you're looking only at the peak - and this isn't really the thing you need to focus on when trying to understand the dynamics of a curve. Maybe a simple analogy would help here.

Imagine a competition between, say, Toby and James. They're going to push on either side of a large block on a low friction surface. The block starts at some point, say A, and the goal is for Toby to push it to some point B. James has to stop him.

We're going to imagine that Toby starts off strong and gets the block quickly moving towards B. James adopts a slow and steady strategy - he knows that Toby has had way too much Christmas pudding and will tire quickly. Sure enough, at some point between A and B (we'll call this point X) Toby tires and the push that James is making becomes stronger than the push Toby is making.

The block still continues towards B, but its rate of getting there is slowing down. At some further point when all the forward momentum has been countered the block reverses direction and starts to move back towards A (we'll call this point Y).

In terms of the curve plotting position against time, the peak occurs at point Y. However, the cause of this occurred at point X, when the force James applied became stronger than the force Toby applied.

In terms of the dynamics of these virus curves we need to be looking at a point before any peaks to get to that "X" point - because that's the point when things fundamentally changed in the dynamics.