I think this is a bad example of what a well executed smear might look like. The recording sounds very unnatural (and one sided).

Further, it is not that different from just making spurious allegations or a meme with a fake quote. However, this is going to get worse and worse in the future. I am glad that the government (who come from the opposing party) decided to confirm that it's a fake. A more plausible version of something like this could be very damaging though.

Audio is pretty hard to fake in general, especially in the UK, who have some of the best forensic audio capability out there (mains hum is recorded in the UK for forensic purposes, and there are other techniques that make low hanging forgeries like this pretty easy to detect) [1].

[1] https://en.wikipedia.org/wiki/Electrical_network_frequency_a...