If I was in your position, I would take a backup of all my critical data and just bite the bullet and re-image the machine from scratch. Sounds drastic, but you will start with a clean sheet - and then only add back exactly what programs you need.

Sometimes it's the cleanest and most expedient solution.

Good luck with it.

Tx. I understand what you mean. I was a user of the earliest laptops in my work and am no stranger to complete reinstalls. But I do not think we are there yet. I have two entirely different modern and fast W10 PCs which have the same problem. Both are kept fully up to date with all program updates. Zen are of the view that the problem lies in the current W10 build. So reinstalling it will not solve the problem.

In reply to a post by JMaples:

Zen are of the view that the problem lies in the current W10 build.

Are they aware than Win10 has been modified by two third party security products? It is no longer as the vendor (Microsoft) has designed?

Zen did not ask about security programs. That is not surprising as they were already of the view that problem lay in the current build of W10. Zen spent an hour and a half on the phone and went into many questions but security programs was not one of them. It is unlikely that Zen would have assumed that I did not have any. Everyone does these days.
But the security programs may be the problem and Zen may be wrong.

In reply to a post by JMaples:

Zen did not ask about security programs. That is not surprising as they were already of the view that problem lay in the current build of W10. Zen spent an hour and a half on the phone and went into many questions but security programs was not one of them. It is unlikely that Zen would have assumed that I did not have any. Everyone does these days.
But the security programs may be the problem and Zen may be wrong.

One thing I'd say is Zen are not an IT support company, I contract for a company that supports over 24,000 users and they've not come across this issue and they support multi gigabit connections.

I have just run a test on my desktop PC as it always runs the latest Windows 10 build/updates.
I enabled the Power Settings and I got exactly the same result on a speed test which is was 630Mbps.
For reference I'm on the Virgin Media M600 package.

Thanks Dan

I think the OP has been sold a bit of a red herring on the W10 powersave ‘issue’ / windows updates issue.

I’m running a couple of W10 boxes, all patched and running latest w10 build and patch and none of them have trouble saturating a gigabit link.

He’s proven hardware on the surface box with both Ubuntu and running in safe mode. His other W10 boxes are displaying similar issues, therefore it it was me, I’d be focussing attention on the security programs. There’s reports about for example of Bitdefender 2019/2020 screwing up throughout on network gigabit links. Full uninstall (and reinstall) being the resolution.

Thanks very much, Dan. Very helpful.

Did you actually disable Windows 10 power settings or just turn them right down?

I have been unable to find out how to completely disabled them?

It doesn't matter what I set them to.
Any changes to them still result in the same speed test result.

Thanks Dan

What a load of tosh.

By using a different o/s, YOU have proved that your isp IS supplying what you pay for.

I use an old laptop with 2.4 GHz (802.11g) and can't get the full speed I pay for.

Should I moan to my isp because they didn't ask what hardware and software I run?