In reply to a post by burble:

Sounds not unlike what has been happening to my connection recently, my answer is the old fall back, switch off the router and switch it back on.

Unfortunately that doesn't work... it all goes up and green looking just perfect and no internet on any of the connected devices...

I'm just confused how come that the router has all the lights green and basically thinks the connection is rosy, but I'm totally unable to get internet on anything from phone to TV...

Does the IP address assigned to the Internet side of the router belong to the ISP you expect, and can you ping that IP using another connection?

Does the router have any pages that let you ping sites or do trace routes, its worth seeing if those work.

Post deleted by XRaySpeX

So to recap:
1) The issue effects all of your devices.
2) Effects all types of traffic, i.e Web browsing & music streaming.
3) Happens after midnight.
4) Occurs on random days.
5) Router power cycle doesn't resolve the issue.
6) Thinkbroadband 'Broadband Quality Monitor' shows no issue.

This smacks of a DNS issue. To prove it,
setup one of your devices to use Cloudflare's 1.1.1.1 new service (there's a handy Google Play store app for Android devices). Then the next time that the issue occurs, if only this one device works, then you can be confident that your current DNS provider is at fault and can then change your router to use 1.1.1.1 (or Google's 8.8.8.8 & 8.8.4.4) and this will then be used by all of your devices in future.