Mike - see Somerset Sump Index 4th Ed p 35-36. The sump was initially dived by Pete Moody for 15ft on 11th June 1978, then on 16th July Dave Yeandle passed the sump (20ft long) into 15ft of small passage, basically ending in a second sump "which was vertical and too tight. At 10ft depth the dive was abandoned as the site was considered too dangerous and with little potential".
There is an aural connection between the Sump Chamber and the passage beyond the first sump.
These places are always worth a second look - particularly 40years later. Enjoy!