I just a minute or so ago added another sentence to my previous post, so you may not have seen that one yet.
The human being who operates the remote button while they are in sight of the garage door is an additional safety feature. So using an automated process which doesn't require a human being to be there is one that is bypassing the safety feature of on location oversight.
To compensate for this, the garage door controllers which are built for this purpose add additional safety features, usually an audible beep and/or flashing light. They also often have a blocked retry feature which will prevent distant operation after an initial failure, intended to address the situation where a person or car is blocking the door. You don't want to keep hitting them after the first time!
When you just hotwire the garage motor so that you can send a request even from miles away that the door operate, which is what cutting in a simple relay does, you don't have the advantage of those kind of compensating features.
I don't know exactly how the engineering codes work in the UK, but in the US a device which can operate the door without the person being there requires a different set of UL safety features than one which is operated just by pushing a button in the same room or in line of sight.