I should update on how things have been since the move to ADSL24.
In a word, fantastic!
Latency has returned to normal, which is about 25ms in the day, 40ms in the evening.
Throughput is also amazing - maxing the connection at ~650KBps peak and off peak.
I was cut off inadvertently due to a billing error, but was sorted over the phone in 10 minutes.
Very, very happy with ADSL24 at the moment.