Can a country (single carriageway) ever be a 70MPH?

Was debating with an idiot of a friend who claimed the road I was on was a 60MPH... because his TOMTOM said so, bearing in mind it's not been updated for 3 years! He also followed it up by saying majority of the traffic do 60MPH on it. It is in fact a dual carriageway with a central reservation and no signs indicating otherwise that it is any other than 70MPH.

I then tried to explain that all dual carriageways with a central reservation are a 70MPH unless otherwise stated via a sign. I also told him all single carriageways were 60MPH unless otherwise stated. This sparked a huge argument and led him to say not all country roads are 60, some are 70 etc etc. He then gave an example of the dumfries road... coming from Scotland I guess this is the A road leading into it. He claimed it was a 70MPH and he has done 70MPH on it because his tomtom told him too and the police seen him and never stopped him. Anyway...

I'm basically just wanting to rant and also reinforce my sanity that this dumfries road isn't a 70MPH? Also to confirm to myself that a single carriageway can never be a 70MPH in the UK anywhere?

He's a **** driver at the best of times... however this fascinated me to the point of wide eyes and a slack jaw.

 

1. It helps if you use a font color people can see.
2. This has nothing to do with General Business.

 

On general chat, best thing perhaps is see what the law/Gov say > https://www.gov.uk/speed-limits