New subscriber woes

[#1]

Makes sense, on 2.4GHz anyway, as they are the only non-overlappping channels - don't know enough about 5GHz to comment.

[#2]

@Baldrick1 thanks for that.

[#3]

@Baldrick1  Thank you.

[#4]

The 2.4GHz channels offered are the ones which ensure no cross channel overlaps and are thus considerate towards all other users.  Why would you want to select a different channel which will cause issues for other users?  Generally, being co resident on a channel is not that much of an issue.  Bleeding over onto other channels is an inconvenience for both you and other users.

5GHz channels above 48 require the operation of DFS to avoid interference with military systems and other legacy users - see List of WLAN channels - Wikipedia

The 5GHz channel signals which are stronger than yours might well be down to a failure to implement TCP (power management) which is an additional requirement in the UK (and EU).  Conversely the lower power seen on your WiFi channel could well be the correct operation of TCP in that only sufficient power is being transmitted as is essential to maintain a stable connection with clients connected to that SSID.

Such is not commonly understood, therefore limiting options enhances everyone's experience.

[#5]

Concerning the strength of neighbouring signals. The router is on the ground floor in a corner of the general floor plan and so is more sensitive to that side of the building. Some of the neighbours are on the other side of the building and can swamp my router. The optimal choices differ depending on where you are standing.
The 5GHz band is a mess with everything stacked on 36 so I chose to go up to 60 where it's clear. What is the point of the higher channels being licensed by Ofcom for use if nobody can make use of them.
My experience is different from another person's experience, so why should a "one size fits all" solution be provided as the default solution? Anyway it's immaterial now as I have replaced the router to one more suitable.