Della:
Camilla converted to the Catholic Church when she married Parker-Bowles who was a cradle Catholic. I haven’t heard that she renounced the Church in order to marry Charles, but it wouldn’t surprise me if she did it privately or it simply wasn’t reported. Shades of Henry VIII.
I thought once a Catholic, always a Catholic, unless you were excommunicated (and I think we’d have heard about that).
There is a lot of confusion about this on the web, but it is hard to get a definitive legal opinion. The Act of Settlement 1701 is very clear on the heir to the throne not being able to marry a Catholic without renouncing the throne.
An awful lot of people assume that Camilla converted when she married her first husband, but I’ve seen no evidence of that, and the fact that she has married Charles and Charles still seems to be going to become King, shows to me that she can’t be a Catholic.
The only possible get-out would be if the legal interpretation of ‘papist’ was ‘
practising Catholic’ rather than just ‘Catholic’, and I don’t believe it is.
Someone would have tested this in court, believe me, if there was any real evidence. In 1953 some Scottish people took the establishment to court over the fact that Elizabeth II should be called Elizabeth I in Scotland, as there hadn’t been a I in Scotland,and this was a putative breach of the Act of Union 1707. It was thrown out, mind

Britain is full of strange people, like me, that are interested in these little things
This article from the Times is relatively authoritative (by which I mean it agrees with my opinion of the law
timesonline.co.uk/article/0,2-1478265,00.html
The other potential complication might have been that the 1701 Act of Settlement prevents a Catholic, or anyone married to a Catholic, from succeeding to the throne. However, while the first husband of Mrs Parker Bowles was a Roman Catholic, she remained an Anglican and therefore the 1701 Act does not apply.
Mike