A few years ago ITV were looking into adapting Warlord Chronicles. Being such a visionary and creative channel, they were very keen on having Sean Bean play Derfel
. Thank god it didn't get made - you can see the idiotic logic, Sharpe is Popular = Sean Bean plays Sharpe therefore Sean Bean should play Derfel. I love Sean Bean, and for all the problems with ITV's Sharpe, i enjoy Sean's characterisation, even if Sharpe is supposed to be tall, dark haired and presumably a Cockney accent, being a Peasant Londoner. The problem is, Sean is too old to play Derfel within the actual stories, and too young to play the elderly Derfel narrating the story of the greatest Emperor we never had to a Princess of Powys. I was absolutely bloody gutted in the books when it turns out that not only did that vile scumbag Bishop Samson continue to prosper, but Derfel is basically his servant/play thing, as a Monk.
Warlord would have suffered badly being made by ITV, exactly the same way that Sharpe did - attempting to tell large stories with a tiny budget - nowt looks as daft as the epic Battle of Waterloo with about 20 Extras!
an ITV Warlord battle, would have been the same, 20 on each side, they didn't even give Sharpe enough of a budget that they could have used some cheap digital tricks to give the occasional overview of a Battle, making it look much larger.
Sharpe's Revenge was it, when Sharpe and Munro are invading France via that strategic border "fort" or as ITV showed it, some bales of wood, ruined wall, and a mighty army of 20 Frenchmen defending the Empire from the Allies, as 20 or 30 Brits storm the place....
If not the BBC making it, then a British company with US Network Funding is the next best option, providing HBO don't intefere with the creative decisions, or insist on American Actors - by rights, and it's kind of the point of the book in a way too, all the Britons should be played by Welsh & Cornish or at least West Country accented actors, and the Saxons etc by English accented Actors. The overarching plot, alongside the story of Arthur, is that Derfel's life started growing up on a threatened but still mostly Briton ruled Island of the Mighty, and as an old man, has witnessed the cataclysmic events which have turned the Island of the Mighty near enough into the set of Home Nations we have today, Wales, England, Irish Scotti invading and occupying the Kingdoms to the North.
I suppose Lancelot and Galahad will have to have French Accents, since we have no idea what a Breton/Armorican Accent would sound like prior to the last 1400 years of French/Frankish influence, but hopefully it will be a modern Breton regional French accent.
I think Ioan Gruffudd would make an excellent Arthur, give him a beard
And you might think me mad, but perhaps with some aging makeup, Rhys Ifans would make a fantastic Merlin!
Eve Miles (Gwen in Dr Who spin off, Torchwood) as Gwenhwyfach, give her some nice red hair. Though knowing HBO it will be Catherine Zeta Jones as first famous Welsh Actress anyone in the US can think of.
John Rhys Davies as one of the Briton Kings, maybe just a quick appearance as Uther
Actually mind, if Rhys Ifans is not suitable for Merlin, I could perhaps see him as Lancelot instead, love to see him preening and chewing the scenery as the arrogant, cowardly ******* of a poseur that Lancelot is in the book. (Bet plenty of people who haven't read the books are going to be outraged at the most famous Hero after Arthur being portrayed as such!)
He is perhaps too old, but Iwan Rheon (Welsh actor from British SFF / "Superhero" series Misfits) and currently starring as Ramsay Bolton in Game of Thrones might make a passable Medraut, if too old, then one of Arthur's Warlords/Companions, perhaps even Galahad.
I suspect the main cast, Arthur, Derfyl etc will be in their 20's, otherwise Idris Elba would make an excellent Sagramor, though as iirc he is an ex Roman Legionary, it might make sense for him to be older than the others, otherwise, there is always John "Star Wars" Boyega as another pretty 20 something
I could see Sean Bean playing Derfel's Father, the Saxon King, Aelle.
The thing that will be frustrating with casting, is if typical casting of Welsh Actors/Actresses or non Welsh Actors/Actresses are hired but are to speak in a Welsh Accent
(if everyone speaks in that boring generic Middle Class, South East England form of Received Pronunciation that used to be mandatory for any British Production, or US production, film or tv made and set in Britain, outside of Soap Operas, I shall be sending some very nasty emails!!! 
)
Then there will be a danger of the usual Accent problems that occur - specifically that anyone playing a character with a Welsh Accent, regardless of origin will put on a South Wales Valleys accent, or even worse, "BBC News Welsh" the Welsh version of the old BBC News Accent. When my Homeland has at least 10 distinctive accents, and infinite localised variations, the accent of people in my hometown for example differs a little from people who grew up in the Rural parts of the area, even if only a few miles outside of town, with the rural accent being stronger, heavier and slower. It's one reason why they need to have people like Rhys Ifans speaking in their real accent, as it will be nice to see a wider range than the generic South Wales Valleys one we are bombarded with - Working class Cardiff has a very different accent to the working class Valleys ones a few miles up the road for example - I say Working Class, for the benefit of any American posters, as throughout Britain you will encounter people from who's accent you would assume came from a "posh" part of South East England, but are actually born and bred in the provinces, but having snobby middle class parents, were never allowed to develop a regional accent. So Rhys Ifan's real Gog accent will be nice, as you never hear the Gog accent on TV. Channel 4 made a TV Series, filmed here in Aberystwyth and in Llandudno, North Wales, and set anywhere in between the two, the Secret World of Michael Fry, but every Welsh accent was South Wales Valleys, despite it being set in Mid/North Wales. It's another thing that the BBC Bilingual Detective series Hinterland, set and filmed here in Aberystwyth got right - it's all local accents.
This is Rhys Ifans, raised in Ruthin/NE Wales speaking in his real accent, which is not quite as strong as a Gwynedd (NW Wales) Accent can be.
And 2 in 1 stone
The dark haired big lass is speaking in a Cardiff (Kairdiff) Accent, the other 2 lasses in Swansea accents as is the older bloke who appears later on.
And the lass on the right is speaking in a Valleys accent, the girl on the left doesn't seem to have a Cwmbran accent, to me at least she sounds generic middle class, the Cwmbran Accent is a strong one
People from South Pembrokeshire, which is as far from England as you can get and be in Wales and a lot of Powys in Mid Wales, which borders England have a weird accent that to a Welsh person at least sounds more like a softer herefordshire/Wiltshire type accent.
