I have heard the John Brune/Old Gypsy woman story from a number of sources - always told from the point of view of trying to make MacColl look like a fool. I always thought that the story had something of an urban myth quality until I read the Sheila Stewart/Living Tradition piece. Certainly, as Jim and Dick have stated, it would have damaged the reputation of the radio ballad if the spoof had been allowed into the finished article. But some interesting questions remain:-

* Why did John Brune want to try to fool (mislead?) MacColl in this way? Was there a difficulty in their relationship?

* Just how good were these spoofs? Certainly Brune would know enough about traveller singing to construct something that sounded authentic enough to fool MacColl? And if they did excite MacColl enough for him to want to include them in the radio ballad, then the surely must have been pretty convincing even if they were not authentic. I don't suppose that these tapes still exist; does anyone know?

Dick goes on to mention Bob Blake, who I knew well, and makes a strong and valid point about him:-
another example of this was Bob Blake who would never have been collected if the collector[mike yates] had known he was not a traditional singer.its time this phoney categorisation was exposed for what it is BUNKUM,this categorisation is about as useful musically as those middle class victorian butterfly collectors
I would agree with what he says about 'phoney categorisation' but feel that it is important to establish the origins of a singer's repertoire in the interests of historical accuracy if nothing else. Here's Mike Yates on the subject of Bob Blake:-

When we first met I assumed that Bob was a traditional singer, similar to the other Sussex singers, such as George Spicer and Harry Upton, that I was recording at the same time. Following Bob's death, his daughter sent me some manuscripts which indicated that Bob, unlike George and Harry, had learnt all of his songs from printed sources and that I, in my naïveté, had unwittingly helped to present Bob as a 'traditional folk singer, rather than as a singer of traditional songs. I cannot stress enough that this article is not meant as a condemnation of Bob Blake, a charming and generous man, but rather is meant to be a re-evaluation of Bob, his songs and my approach to him. It is as much a critique of myself as it is of Bob.

This is part of the introduction to an excellent article by Mike at http://www.mustrad.org.uk/articles/blake.htm
Following on from this is the question - Was Bob trying to mislead Mike Yates into believing that he was a traditional singer when he wasn't? Answer a firm NO. Bob heard the likes of Pop Maynard, Harry Holman and George Spicer in the singing at old Sussex pubs like The Cherry Tree at Copthorne, loved it and wanted to learn songs that would enable him to be part of the crowd - and he knew where to look for them. He found the tradition and wanted to join in - no ulterior motive.
From a personal perspective another question arises - If we had known that Bob Blake had learned his songs from printed sources, would we still have included him in the 'Sussex Traditional Singers' Evenings' along with the likes of The Coppers, G. Belton, G. Spicer, G Hall, J. Doughty, L. Fuller etc. etc. that we held frequently at our folk club in Lewes? Answer a firm YES. Nothing that the ear could detect would have put him - in terms of style and repertoire - in a different category from the other Sussex singers.

Collecting folk song in the mid-twentieth century was a minefield and inevitably meant that the collector was likely to record items that had been learned from media or folk revival sources. In Mike Yates' case there items released by Duncan Williamson and Joe Rae that fall into this category.