As you probably know already, the main language of the UK is ENGLISH, seeing as ENGLAND where it originates from is one of the main countries that forms the United Kingdom.

The #1 resource for accurate spelling & usage of English (UK) is the OXFORD ENGLISH DICTIONARY from the Oxford University Press. This is available in traditional book form, Online & as an APP for your iPod Touch, iPhone & iPAD.

But there’s good reference sources from other publisher too, such as COLLINS, etc.