Eureka!!! - but I don't know why!
Had a long session on the 'phone with the next level of help, plenty tried, nothing resolved, elevated to an even higher level and told I would be contacted in 5 - 6 working days but this morning all is up and running as fast as it should! I guess they found a problem at their end?
Thanks again to everyone who has contributed and in particular to Keef and Saab Dastard.