It's odd that this has come about, especially with the change in which TL is determined, which was introduced earlier this year. In 30-odd years of working in our TMA, I never once passed or was even asked for, the TL. We operated using 'Minimum Stack Level' which always gave at least 1000' separation from the Transition Altitude, and is the basis of the revised procedures mentioned above.
I can't see a big issue here, according to CAP493, you only pass the TL if an a/c requests it, so it seems reasonable that it should be correctly read-back.