I know the very recording you mean. I must admit McColl had a point but I think he was a bit harsh. The use of portamento was still audible to me, and that is part of some Gypsy's style of singing.
Mike Yates pointed out a real howler to me, when McColl pointed out that a singer was uttering 'The Merrier Gods' in a carol, when in fact he was singing the Merry Organ. Still the Song Carriers are unsurpassed in my view. I'll work out a way of getting these recordings to you.