"I need a British English Voice over for my project."
"Why do I need a British English Voice Over Artist and not an American, Canadian, Australian, New Zealand voice over artist?"
In the voice over world type of English that is usually the most sought after is still this powerful announcer or documentary styled voice, there are many other types of English voice and more likely than not nowadays a more natural British voice is preferred for some projects rather than the stiff upper lip from the past. The voices in England, Wales, Scotland and Northern Ireland are all different but still English. The accents that are apparent in all areas of the UK are many. For anyone who has spent some time in the UK you notice that within every 30 - 50 miles you can run into many different accents, so much so that the English people who live there have problems understanding their own colloquialisms. In Nottingham, my old home town, a cob is a bread roll and a cob in London is corn on the cob, so you can see with this one example even the British English voice born straight from the country where it is used can be different. There are other examples but I will not list them here. That being said the British English voice over artists are voice over artists because they have broken away from the mould and standardised their accent and colloquialisms or used them as a selling point. However, there are roughly three main types to speak of, BBC English, Shakespearian type English and more higher energy street style guy next door style English. There are other types of English but for your projects you will mainly come face to face with these types of English voices unless you specify you want something different.
When thinking about your voice project you need to assess what kind of British English voice over you need. The diversity of an British English is so much so that you may need to audition a lot first to see what fits into your movie, advert, the reading of a poem or any other preferred read. Maybe you don't even want that British accent, maybe a US, Canadian, Australian or Kiwi English accent could be more preferred. This is all down to personal taste and I would say personally from what I have heard, a documentary with a British English accent is usually more highly respected than a US accented documentary voice over, think of David Attenborough (The Blue Planet) and Sean Bean in the documentary (Decisive Weapons). Both of these English men have English accents but both are completely different.
Depends on what the content of the video is to choose your voice artist and maybe for a commercial voice over fast and furious could require a US voice over but not always. Not since the Boston Tea Party are the English fighting back and some are actually fighting for and winning more voice jobs now than was ever possible in the past. This is due to the fact that the voice industry is now more global than ever and US producers do prefer the voice of a real Brit occasionally. Of course, the same can be said of advertisers in the UK preferring a US voice to show their product has street cred or showing that the product they are selling is a sure fire hit in the US too.
Back to the English voice, think what your project will need most out of an English voice over, high energy doesn't always mean a US voice over and documentary doesn't always mean British English voice over, all voice overs for all markets can be produced with a British, American, Canadian, Australian and New Zealand (Kiwi) accent but if you have something specific and you want a specific type of voice, similar to a well known character like James Bond, Rambo, Wayne's World, Crocodile Dundee or a Shortland Street character then it is usually best to go with the type of English voice the character was originally.
Don't forget the beauty of getting auditions for voice overs is that you may have a type of voice for your voice project in mind but when you finally listen to all the auditions sometimes you may change your mind, this can be for many reasons, quality, lack of background sounds, warmer sound, deeper sound or just a complete change from a US to a UK English, a NZ to AU English voice over, etc. The end decision is always in the production house but sometimes a change in what type of English you are going to use in your project could be the game changer your project needs.