Roy,
This whole situation is becoming more troublesome with each passing day.
Today I received news of 3 freshly sleeved guns from a highly respected specialist all failing proof with bulges behind the chokes.
Understandably the specialist asked for an investigation and the Proof House has offered to do the subsequent tests using old proof cartridges from a previous supplier. I have an interest in this as I have several guns in the log jam from this situation and I am crossing my fingers that all will be well.
It would appear from this development that the London Proof House has tacitly admitted that there is something amiss with their proof loads although the are admitting nothing verbally.
The problem with what you suggest is that the Proof Houses are very much a self contained, self regulating institution. If they brought in outside help, they would probably see that as an admission that they are not up to the job, something that I doubt they would be prepared to do.
Furthermore, if they had been at fault, they might be at risk of becoming liable for all the damage they are currently causing. Again, not something they are likely to relish.
It would appear that this current difficulty is centered in London, I have heard from 2 sources that Birmingham were unaware of London's problems.
Give me strength!