Martin,
That's an interesting question, and today there may not be an exact answer.
The gas regulations specifically exclude the regulator, flexible piping and bottle top fittings, so that the user can exchange bottles and regulator if necessary. But these were written for the previous bottle mounted regulator, and need redrafting for the fixed regulator
So you could argue both cases, that the BS EN 1949 bulkhead regulator is covered by the user replacement exclusion, or that the connection between the fixed regulator and the fixed pipework means that it's inside the competent person framework.
Or maybe I've missed an annex to the 1998 gas regulations which covers this situation.
And competent person means someone who's completed the approved training course and has the relevant professional qualification (bottom rung is HND)
Robert