OK, so, forecast vs actual outdoors, and inside the polytunnel.
Fri Forecast 3C, Outside actual 6C, Polytunnel 8C
Sat 2C 3.9C 5.7C
Sun -1C -1.5C 0.6C
Mon 2C 2.6C 4,3C
So, the forecast was pretty good, and it looks like a fairly steady 2C difference in the polytunnel over the outside. Looking at those as well, I'm glad I brought the tender plants back into the house.
Unsurprisingly, coldest temp was dawn-ish, around 5-6 am.
Daytime temps peaksed at around 25C, btw, around 15C warmer than outside, when the sun was out.