HSE Requirements changing tyres on Trailers

Hi all,
recently broke down and was asked to change out a blown tyre on bulker trailer (blown out air bag same tyre as well). I ended up with ATS coming out, the lad enquired If I was attempting to fit the very ropey spare provided on the trailer - well yeah

He then proceded to explain that this was now illegal and could only be done by a competent trained person - Is he right on this, Ive asked around other drivers and quite a few have agreed with this !!

So my question being - is this now law !!

I doubt it’s actually a Law as such, but no doubt if anything goes wrong either in the fitting process or the wheel coming off the HSE or insurance company, might ask the company to prove that they got a competant person to do the fitting, and in these days that means a certificate.