Here is another weather report from Chepstow..

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At 7am it was minus 6 to minus 7 depending on location

Still well below freezing now, minus 3 at 9.55am and the van is in full sun...so probably more like minus 4.
About 30 minutes ago I cleaned the windows on the house I live in, water freezing up all over the place, on the glass in some parts, on the sills and on the floor.
Bristles on brush iced up as I was winding in the hose, and girlfriend [who works with me] has just checked out the van, and brush still all iced up

so unless there is some way of preventing the freezing it's a day off al round..sigh.
Another forum member local to me (Tomo...not sure what he calls himself on the forum though) has found somewhere local we can get Isopropanol from (£50 for 20 litres) and he's bought some to try with his system.
Waiting to hear back from him to see how he has fared today.
If he is successful then it is a way to keep working, wil also be interesting to see if the isopropanol evaporates out of the water leaving the water to freeze on the ground....questions questions and not enough answers!!
Cunningly I thought that as WFP would be no good to do a couple of shops we had to do first thing, I decided to do them trad....but first to get some screenwash to pour into the water to stop the water freezing up on the glass....Tesco had sold out, non in sommerfield or the local spar, found a litre in a garage forecourt...but after losing an hour farting about finding the stuff it was still no sodding good...the water still froze up on the glass

Perhaps the stuff I got just wasn't concentrated enough....
Ian