Hey wardrobe
My ph is around 6.2 but that's for hydro, I believe dirt is the same. The small containers might be making them root bound. probably best to wait till the next grow on that might stress them too much. here's a site i find very helpful:
http://sharprubberduck.com
Ph of 7 will slow down the intake on some nutrients so you might want to lower that. Try slowly at first [6.6] wait a week, see how they respond, lower them a little more till you get them to 6.2 or so.
As far as UK based nutrients, sorry I can't help you out there, possibly a hydro shop there will have some.
You have a good handle on things, far better than I did on my first grow , my hats off to you.
hope this helps
peace
heart