I believe there is an issue here - essentially BS EN 61439 has that the main switch should operate on - in an upward direction, and it does not in this case, so even if the manufacturer doesn't specifically state anything it ought to be implied.
However I would check with the manufacturer themselves, Hager specifically state that they must be installed in the horizontal plane only, and from memory I have seen it with others as well.
If the manufacturer has stated a direction then it would warrant a C3 to me, if not I don't think there is sufficient justification to argue the point even though it is implied.
Now moving forwards with amd 1 and the 18th I think there are further issues - the principle of the compliant enclosures (BS EN 61439-3) is not just the material (the really, really ought to be metal thing), but that the enclosure should prevent movement of flame forward outwith the enclosure, which implies that the door should also ensure self-closure to enable this.
Now it isn't directly in BS EN 61439-3, but BEAMA have stated in their technical bulletin that the standard describes effective control of flame by having a case, a cover and a door in place.
... And that if the door may be left open, then in effect it isn't compliant.
Obviously this installation predates this, but is the case for anything since 2016
(and of course this metal and so on restriction only applies to homes, not commercial etc)