I would simply remove and reinstall the Sonos Skill in the Amazon Alexa App - it sounds like the sharing agreement token has just lost its connection between your Amazon & Sonos accounts.

Hi

Thanks, I’ve done that several times and the issue is with every service provider, Spotify, Amazon, BBC, etc. All of whom I have removed and re-installed with no improvement. It worked fine for a year, now this is very frustrating to me. 
Thanks again for the response.  

I’ve just tried asking for my morning briefing and again, I get the response  “John, here is your morning briefing” and then nothing…...

Still sounds like the Sonos Skill to me - try removing the skill and also deregister each of your sonos devices in your online Amazon account (under ‘manage my content and devices’). After all are de-registered you need to reinstall Alexa on each of your speakers through the Sonos App again - this will automatically re-enable the skill and re-setup the sharing agreement.

I’ve added some screenshots to my last post, taken from my Amazon account to show you what you need to look for in your online Amazon Account to deregister each device.

Hi again 

Although we have different screens on our iPad over here I have carried out as you have instructed with no avail  perhaps I should delete the whole system from everything (ie apps from each iPad / iPhone etc ) and start all over again. Pretty poor though. 
Thanks once again for your time - why can’t we contact Sonos any more with our diagnostic info do you know?  

 John. 

You should have the same screens - I’m also from the U.K. - are you looking in the right place to deregister your sonos devices from the Amazon account (after removing the Sonos skill)… it’s in the Amazon account online at amazon.co.uk?
 

On login, you need to goto “Manage Your Content and Devices” off the sign-in menu and select ‘Devices’ tab at top of screen?… it will automatically remove all the devices from your Amazon App when you do this (deregister each one)… then just add Alexa to each one of your Sonos speakers through the Sonos App. It will restore the Sonos skill, sharing agreements and all your Sonos devices to the Amazon Account.

Sonos Customer Care can be contacted here if the problem persists:

https://support.sonos.com/s/

I’m back! I’ve been through your steps and I thought I was making progress but now I get tge “hmm, to do that……….discover devices…...” line now. I have tried that but with no success. I feel you have helped me 98% so far, any chance of the final 2!?

I really appreciate your time here  

John  

The screenshot of your Amazon account Sonos devices, looks like it is showing the Sonos Speaker "Alexa Component", but not the actual ‘Speakers’ ...Have you perhaps (ever) renamed the Alexa Component part of your speakers in the Alexa App device list at some point in the past ?
 

It looks like you may have given each Alexa component the exact same name as each of your Sonos speakers. Perhaps that’s why you are having the issue?

There are two components to each speaker that has a voice assistant built in. You should see two entries in your Amazon Account. One device for the Alexa part of the speaker and one device for the speaker itself - they should have different names. So your three speakers should have two devices each - you are missing the speaker component.

Try this - ask Alexa to ‘scan for devices’ and see if the speakers show up in the device list. Note their name should ideally be different to their corresponding Alexa component.

In my case, just as an example, I have a Sonos Beam called "Dining Room” its Alexa component is called ”Sonos Dining Room Alexa” so just ensure they are named differently and that you have a total of 6 devices for your three speakers (that’s assuming you have Alexa on all three). You will see all these devices too in the Amazon Alexa App device list, so can view them there too, save you keep logging into your online Amazon account.

I should have perhaps mentioned that in the Amazon Alexa App, an Alexa component device (when Alexa VA is installed onto a Speaker) is sometimes shown embedded inside its associated speaker device, so you may have to select (click/double click) the Sonos speaker in the Amazon device list to see its Alexa component device.

On the Amazon website however the two are always listed as separate entities.  
 

Hope that also helps.

Hi Ken

its working (with a few oddities I can live with!). I’m not sure how but yesterday it point blank refused to search for any speakers insisting there weren’t any at all. Then the lounge beam, sub and ones started obeying but not the Move or the spare room etc. I de-registered everything once again this morning and hey presto it worked, I’ll take that. 
Thank you for all your help, I’ve learnt a lot  and should something go wrong again I feel I’m in a much better position to correct it. I’m still at a loss as to why it stopped working after a year of faultless performance but let’s put it down to another 2020 oddity! 
Thanks again and if you’re ever at Appleby Golf Club the beers are on me!

John  

Ah that’s great news John - I can see from your screenshot that all your devices are now showing in your Amazon Account. Glad you sorted it. Thanks for the beer offer too ha ha 

Have a good Christmas & New Year.