Yep, I was thinking about the equipment earths that are on the clean mains supply side. Connecting then to the centre tap makes good sense and allows for fault currents to blow fuses which is good, but should there not also be some sort of connection to mains earth to avoid possible electrostatic build up of potential between to clean earths and the mains earths?

On the one hand it seems this is needed for safety and on the other avoided for purity. Perhaps just some kind of choke would do the job?

Yes JMS are in Ivatt way, sort of between Peterborough grass machines and Radical motorsport, there is just a plain looking door with a combination entry lock and a push button. Just turned up without notice and they were pleased to help. AKAIK they don't do audio transformers or small power toroidals but make anything from the little 25VA up to sub-station stuff. The website gives some idea, but I think its always best to visit when having custom stuff made.

We are looking at about 3 working days before collection, two units only no problem.

Edit: JMS do toroids and others according to their site, just did not see anything like that during factory visit.