I concur with dragonchild in as much as this should be treated as any other piece of language translation, and can't be managed by a translation dictionary alone.

However I'd disagree that "outsourcing" to India is a viable solution -- in any translation work you should only translate into your native language, and this would be particularly true for the case of US -> UK English where nuance is important and where pop culture English is dominantly the US version.

The detailed requirements will likely vary a lot depending on the nature of the work being translated and its intended purpose, in many regards scientific or technical material will be the easiest to translate (though this will often still require significant work -- my father worked for several years with a team that translated RAF technical manuals from UK English into US English for the USAF) anything using idiom, allegory, wordplay, etc is likely to be far more problematic -- the traditional "beauty versus truth" problem here manifesting as when do you faithfully preserve the text and when do you interpret its meaning.