Yeah HDMI CEC is just too convenient to turn off. It’s just frustrating that the IR sensor works perfectly and then just stops working randomly. It wouldn’t matter if I programmed other remotes it’s the beam that doesn’t receive IR commands. 
I might try a small piece of tape over the IR sensor. That’s all I’ve got left to try to be honest. Hopefully this will stop any excess IR interference and stop confusing the Beam (if that’s really the cause!) 

If your pad/phone camera is sensitive to IR, you can verify that your remote emits IR.

Could you enlighten me on this please? 

Attempt to take a picture of the remote’s emitter while emitting a command. While previewing the image you may see a faint flashing. First you need to verify that you can see some flashing using a remote that you are certain is emitting IR. An older CD or DVD player remote would be a good test candidate. Modern TV and cable box remotes might use Bluetooth to communicate with their box. Another way to prove that IR is being used would be to physically block IR transmission. If commands are no longer executed, then you know that IR is being used.

UPDATE. Power cycled the Beam and Sky remote working via IR for music streaming volume and HDMI CEC for TV volume. I’ve put a strip of sellotape over the Beam’s IR sensor to reduce any sensitivity/interference.  So far so good. Working perfectly. It looks crude but could be made neater if it works long term.