So it seems it is not 'just about' the wedding, but other implications
''Apparently the catholic church states that if a catholic marries a non catholic in any marriage not conducted by the catholic church, the marriage is not recognised as valid. By accepting those terms in order to proceed with his marriage, Johnson is accepting that having been baptised a catholic, he not only still is a catholic, he has always been a catholic.
This has important constitutional implications which I am sure will not have entered his head. Firstly, he has just "come out" as the first catholic Prime Minister in the UK's history.
Secondly, there are certain functions which are the sole responsibility of the Prime Minister which Johnson, as a catholic, is actually barred by law from performing.
The one which come immediately to mind is that under an act passed in the early 19th century and still in force, no catholic is permitted to advise the Queen on the appointment of any office holder in the Church of England.
Any catholic doing so is immediately rendered ineligible to hold any office under the crown for the rest of their life. This is where it gets interesting. Since Johnson became PM, a new Archbishop of York and at least one other diocesan Bishop have been appointed.
The procedure for such appointments is that a committee of the Church of England select a nominee and forward the details to the Prime Minister for approval. This is not automatic. Margaret Thatcher turned down one nomination for a bishop when she was PM. Assuming the PM is agreeable however, they advise the Queen to make the appointment. It would appear therefore that Johnson, a catholic, has advised the Queen regarding at least two appointments in the Church of England contrary to English law, and is therefore barred from life from holding any office of state, and is consequently no longer Prime Minister. I await developments with interest.
I think we should all speak out in mass, not just the Pope. As he is well over due a comment on the UK's human rights issues alone. As now even Amnesty International have Johnson and his vile Conservative Government on their list.''
as explained by an expert responding to an article in The Telegraph.
