A variety of reports:http://www.bbc.co.uk/news/uk-12048598 and http://www.telegraph.co.uk/news/ukne...-Pakistan.html

A mixture:http://www.telegraph.co.uk/news/ukne...d-in-jail.html

From which:
Muslims leaders said they tipped off police about the group of extremists in the Welsh capital, where five men between the ages of 23 and 28 were arrested. They said they had stopped the group from holding meetings in mosques in the last month and told them to "go elsewhere."
Mosque officials informed police but it is thought that MI5 was already aware of the group.
I know of one analyst who is puzzled that amongst the 'Xmas Twelve' are reportedly five Bangladeshi's, who went for training in Pakistan.