Can anyone recommend a good reference book about Celtic Christianity?

Celtic Christianity is not what you say it is. It was the version of Christianity that existed in Britain and Ireland. I don't know what meeting you are talking about, it sounds like an innacurate telling of the Synod of Whitby. But books;

Life of St Columba by Adomnan of Iona.

Land of women by Lisa M Bitel

The book of leinster circa 11th century

but then you may not want to read them as even though they are primary sources they have been recomended by an atheist.

@Captain, stop talking rubbish. Everything you said was wrong. the Celtic church was the name given to church based in ireland, Dal riada and northumbria that survived apart from rome until the norman conquest of Ireland.

The Celtic cross is indeed christian, it however borrows a pagan sun symbol. The pyramids were thousands of years prior. Put down the copy of zeitgeist and read a book.

The Celts were not Christians, they were mostly druids and atheists.

It was only in the 10th century that they became Christians.

The Celtic cross has nothing to do with Christianity, instead it is a navigational device, in fact when Constantine saw it he decided it was the perfect symbol for Christianity this was around 667AD.

Without the Celtic cross the pyramids would have been impossible to build.

A am an atheist but it is far better you know the truth, than going up the wrong path.

bother bother

art thou mad, brother