I went to halfords in the end. I know you always overpay in there (I have a trade card so it's not the worst) but it's handy when you need things sorted and running,like, now
My searching of pats guide on fitting the ivans ais kit turned up that the coolant I needed was an ethylene glycol based anti-freeze with corrosion inhibitors for an aluminium engines which is low in silicates.
So I got the silicate free version of halfords coolant which is also ethylene glycol based. (I bought the 50% mix as it saved faffing but they also sell concentrate.)
Just thought I would include that info incase anyone else stumbles on this while searching.