Phil Edwards said
As for Bert Lloyd, I think the reason we still scratch the 'Bertsongs' itch is that he could have done English folk song a great deal of damage. If the approach which (I believe) he took had been more widely adopted - if it had become normal for singers to thoroughly rework songs in the way that he seems to have reworked Skewball, The Mountains High, The Yahie Miners, Jenny's Complaint and others, and to pass off their own rewrites as contributions to the tradition - at best it would have caused a lot of confusion; at worst it would have undermined the whole idea of a traditional song. The reason that didn't happen, ironically, is the same reason people still sing those songs in their post-Bert forms - unlike most folk singers, Bert Lloyd was a damn good writer, and when he rewrote a song it stayed rewritten.

and Dick said
correct, he improved the tradition, this is something that has happened to trad songs for centuries.
generally speaking improvements to the tradition that are not good, do not survive, the "folk" sort that out, so why all the fuss about "Bert",
Scholars are well able to sort it out,and singers like myself consider the merit of the song slightly more important.

I agree with Dick, except on that last point, where Lloyd's obfuscation of his sources makes the sorting out difficult and leaves singers and listeners still suffering from some false beliefs.

That is really the only respect in which what Lloyd did differed from what loads of people have done for centuries and continue to do still. Most often they have simply offered a rewritten song to the world, saying nothing about where it came from, which is OK. Nowadays it is more common to explain what they've done, which is better. Lloyd rewrote songs and attributed them to fictitious persons, which was dishonest.

In some instances, his motive for doing that was clearly political: when he couldn't find enough evidence of songs by and about industrial workers, he invented them. In other instances, he may just have been concerned that, if he admitted rewriting a song, people might reject it as inauthentic and therefore worthless.

People do worry about authenticity, even if they can't define what it is. Coming back to Phil's comment: the idea of a traditional song is very susceptible to being undermined.

One friend of mine, attending one of Steve Roud's courses, was devastated at being told that so many of the collected songs that we love had started life on broadsides, in the pleasure gardens, on the London stage, etc, rather than getting into print only after being made by the peasantry. (Pace Jim, we can have different opinions about the respective proportions, which no-one knows for sure, but certainly a lot came originally from professional, commercial song writers.) Steve hastened to re-assure her that what matters is not where they started but the fact that they were subsequently sung by and collected from ordinary people.