Immobilser bypass

[OlderMan]

I took possession of a non-running 2003 Megane DYNAMIQUE 1.6 16V, three weeks ago. I had proper look at it this weekend.

It is in good condition mechanically, trim knocked about a bit, hole in the plastic wing, all things I can fix. It just won't start.
I had a roving mechanic out, with a big box of diagnostics. No faults recorded but still won't start. He confirmed nothing wrong mechanically though. The finger was pointed at the ECU but after speaking to https://www.the-ecu-doctor.co.uk/, free of charge, he has advised to try the immobiliser first.
Now, there is an awful load on the Internet about bypassing immobilisers, getting codes and inputting via different buttons on the dash.
I even found an article from a Renault mechanic that this is all correct, just dealerships don't advertise it, as it has security implications.
It all seems to be pre 2002. The immobiliser expert in Glasgow says it needs to be brought to his garage (towed) and only then can he maybe fix it.

I don't mind, if I could be sure it is the problem. I have spent about £150 so far, if I get it to the immobiliser garage it will be another £150, before I even take it for an MOT. It will still be a bargain if it gets through the MOT but there is no certainty about that.

Does anyone know about these immobilisers, even short term to get the car working so to get it MOT'd? Then I will know how much the whole this is going to cost me? I'll be getting my daughter, the Register Keeper, to go into a Renault Dealership, but I feel I know what the answer will be. Anything to help with that conversation would be helpful also.

Regards,
Colin.