All is sorted out - BT number working again, separate VM master socket installed, everyone has been as nice as pie and falling over themselves to get it working properly.
But I feel very bad because I've been told the engineer (who was a very friendly polite guy) has been hauled over the coals for what he did.
If the Sales people had arranged the number port for the same day the engineer visited, I reckon everything would have worked out as expected and I would have been happy. Just very bad luck I guess
Having read another website about how the terms & conditions Avonlink contractors work under, I feel doubly bad.