Has any Catholic been knighted by GB in recent history?
Yes.
For example Catholic composer James MacMillan knighted, 2015.
Also atheists, Moslems, Jews, Hindus etc, the honour is not reserved for people of any specific faith.
a headline about a Catholic geting knighted merited mentioning that he is, in fact, a Catholic
That may be because I found him by searching for something like "Catholic Knighthood" - it was likely that the first relevant headline
would include my search terms.
Although he is a well-known Catholic, noted for its influence in his music, you have to search hard to find anyone else who considers Macmillan's Catholicism worth remarking on in the context of a knighthood:
- UK Gov: The Queen’s Birthday Honours List 2015
Dr. James Loy Macmillan CBE. Dr. Macmillan is a composer and conductor of international renown. He has retained his distinctiveness as a composer inspired by religious faith and he is also active as a working parish church musician in education and community work. His music was the focus of the
London Symphony Orchestra’s 2009/10 Artist Portrait season, where his violin concerto was premiered alongside performances of his trumpet concerto
Epiclesis and an education project Into the Ferment. He has served as Composer/Conductor of the BBC Philharmonic and remains Principal Guest Conductor of the Netherlands Radio Kamer Filharmonie.
- BBC Scotland: Scots recognised in Queen's Birthday Honours
Scots from all walks of life have been recognised in the Queen's Birthday Honours list. They include composer James MacMillan, who is to be knighted
- Music Newsmedium: Classical musicians recognised in Queen’s Birthday Honours 2015
James MacMillan, Karl Jenkins and Simon Halsey are
among the classical musicians to be recognised in the Queen’s Birthday Honours list for 2015. MacMillan, who was made a CBE in 2004, has received
a knighthood for services to music. The composer, conductor and festival
director considers his Scottish roots to be of great importance; the first Cumnock Tryst festival took place in his Ayrshire home town last year, and his works bear the influence of Gaelic folk music.
- Scottish Christians: James MacMillan leads knighted Scots
Composer James MacMillan has said he is “totally delighted” at being knighted in the Queen’s Birthday Honours list.
The 55-year-old has been awarded the honour for services to music.
Dr MacMillan’s music is widely performed around the world by performers ranging from top international orchestras to local church and community choirs.
One of his compositions was a new choral piece which was sung when Pope Benedict XVI conducted mass at Bellahouston Park in Glasgow in 2010. ...
[no explicit mention of Catholicism]
It seems that regional or niche media tend to mention that the subject is "one of us", even when it would otherwise be unremarkable. He's not the first musician to have been knighted, nor the first scot.
This actually makes it harder to answer the original question. You can't tell if no blue-eyed left-handers are allowed to be knighted - because those factors are almost never reported. More likely they are not reported because thay are not relevant or significant (in this context) than because there is an anti-blue-eyed-left-hander bias or rule in the UK establishment.