Thanks for the help received. Problem solved. I used a Shelly wi-fi controlled relay. Very simple and straightforward. My only observation would be that whilst the Shelly module fits inside the Rolec box very easily if I were to tackle this again I think I would bring two 12v wires out of the Rolec box and into a separate junction box with the Shelly and a power source. This would enable fitting of a bypass switch and easier swapping of the module if it is faulty or as in my case, to be reset to a different Wi-Fi signal. But all in all one happy bunny - £16 v cost of a complete new smart charger - no brainer.
I have bypassed my Shelly now inside the Rolec as the Gen 2 model does not require it of course.
It is still powered up, but is not activating the comms unit.
I was in the garage at the weekend and decided to see if the Shelly was still energising, from the App on my phone still.
Yes - Sure enough, I could still hear it clicking away inside the wall box after about 18 months of being installed.
The Sonoff relay does have a manual over ride push button on the out side of the case, but is still not readerly available, while being living inside the casing.
You are correct of course, with the Shelly wired in place, you have no manual over ride to command the wall box.
Your idea for the extra enclosure is a great belt and braces approach.
What about the idea of fitting a deep / single stand off back box, close to the wall box.
Deep enough to install the relay, then fit a simple single switch plate and wire it to allow manual over ride to the wall box ?.
Glad you are all sorted !.