I’ve recently decided to give up my mobile and rely on my landline (which is being upgraded.)
When I got my mobile, I chose a memorable number (it cost £5.)
Apparently such numbers are valuable 
I’ve had an estimate of £1,000 for mine. 
I’m in the UK - can anyone recommend a reliable company I can sell to?
I asked an AI for an answer and got one that seems correct on how to do this (it says it is possible) but I am unsure if we are allowed to do that (especially in FQ). Please advise.
Moderating
Since this is more help and advice than factual, let’s move this to IMHO (from FQ).
AI is very good at posting something that “seems correct” even when they are completely wrong. You can post it, as long as you clearly indicate that it’s AI generated, but we would prefer that you actually check the AI’s cites to see if they really say what the AI bot thinks it says.
In other words, AI can be useful to get you to an answer, but don’t use AI alone for the answer.
Given the above I will only share what the AI offered as sites you can check to sell/buy mobile phone numbers in the UK. There was a lot more advice and caution about this process but I cannot verify all of it so skipping it.
This (below) was provided by my AI. I checked each site and they all exist and work. Beyond that I cannot vouch for them:
AI answer:
Brokers to start with for a valuation: Numeros (numeros.uk), Numbers Market (numbersmarket.co.uk), and easydigits (easydigits.co.uk).
Thanks - I’ll check those sites out.