See the Zaino Z7 has 'gloss enhancers in it which compliment the Zaino sealants, but it's quite expensive for its dilution ratio.
I'd have a look at something like Dodo Born to be Mild, which again you can't get from Halfords, but its more concentrated than the Zaino and works better with waxes (although yours is a 'hybrid' technically speaking).
Most of what is competing for shelf space in Halfords is bulked up, poor dilution ratio'd, stuff. Megs Soft Wash Gel (pink stuff) is okay if you can get it, or the Zymol Auto Wash if you can find any stock (it's been pulled from Halfords!).