Well I tried the 'heavy' approach, and it worked to some extent; in that their speed increased from snail pace to turtle pace.
( . . . and I absolutely hate doing that . . . acting the bully is not my scene . . .)

Sooo . . . onto the telephone yesterday and an ultimatum was issued: Have it done by the end of this month, because that's when it's being pulled out, finished or not. I can't afford the time to have it sitting while we're overseas.
It must be in the paint shop before the 7th June; because that's when we fly out.
(We don't really; we fly out on the 23rd, but they're not to know that.)

The response?
"Oh! Well it looks as though we're going to have to work weekends then."
To which I replied: "Bide a wee here mate; I think you're confusing me with someone who gives a s**t! Because it's coming out 3rd or 4th of June; depending upon when I can get an appointment for a Certificate of Fitness booking. End of story."

So that's the deadline.

I've already spoken to Frank Bruyston of Thames Towing, just down the road from the Testing Station, who told me that if I needed any mechanical repairs for a Cert. I was welcome to use his tools and facilities.
(Frank's a member of the N Z Morris Minor Club . . . has a Morrie with a 350 in it, and a good bloke. Sometimes it's not what you know; but who . . . )