I'm guessing that these need to be constructed and painted? What scale are they?
Yes, they're pretty much regular plastic kits, although some have motorised features and contain parts for motorisation. Some offer screw together components, the big TB-2 has main parts that are screwed as well as glue. Scales are variable.
Are they not sold in the UK, as there appears to be writing on the boxes that I cannot read?
They originate from Japan and have Japanese text on the boxes. They are fairly limited in availability in the UK/Europe, I've been ebaying some (you might be able to buy direct in some cases), others I've been getting from a couple of Facebook sellers who order them in if they become available.