XD that does work too. Brits have a way of speaking though. Their style is different than America’s so keep that in mind.
Highly personal opinion in this post, but I'm not fond of "faking" so-called British English. Not only does it often turn into a sort of blanket stereotype, but imagine being British and reading sum feeked acc'nt when you literally have a common language, but with distinct spelling, vocabulary, and grammar. I'd suggest using that instead of othering the British readers by making them talk a bastardized version of their own language.
It's also weird to read a "British accent" when you're not from author's country of origin in general (let's assume US for now). I mean, think of it. I first of all need to assume everyone is speaking American English by default and then paste the accent on top of that default.
The exception, I think, is if your character has an accent that is distinct enough that a native Brit would write it differently - think Hagrid (apparently it's West Country English).
Basically, what I'm trying to say is that an accent is relative. It's default to the speaker, and only an accent to a foreigner. When you modify sumthin' it's making an assumption about the reader's default language. Look at it from both sides instead!
Just my take on keeping it international.
(I'm sorry if this comes of as a bit negative, that's not my intention.)
Those we're all fantasy races, so I had a bit of wiggle room. I avoid idioms and other figures of speech when I write, so it's really a sort of Standard English with a lacquering of Britishness.
okay, posh accents, theyre honestly not that different from american textually - just very formal, and no americanisms. maybe get a british person to proofread your dialogue?
try making a thick Yorkshire dialect accent nobody will understand him and you could literally write gibberish and it would make sense XD
in all seriously accents are a bit tricky to convey when they all speak basically the same language so look for what different things the others say, examples like bum and fanny or biscuit and cakes, also you could try writing them in the different orthographic styles a classic example is color and colour
It’s difficult to convey a British accent purely in written word. So many British books have been adapted into American movies with the location changed to America using American actors and you wouldn’t know the difference. The character’s mannerisms would probably be more telling, but I don’t even know where to begin with that!
Depends highly on which part of the UK they are from obviously...
Certain vocabulary would clue in a lot, such as slang words. Different slang is used in different parts of the country...
E.g. I'm from the south where we are descended from sailors and farmers, and we call people "love" to be flattering, say stuff like "innit" and use hard "r" sounds.
My friend is from the north where many are descended from miners. He uses words like "pal" and his "r" sounds are soft. Think John Constantine - he's from the north.
Funnily enough there's a few slang terms we share. It's weird.
I'd recommend looking up some footage or audio of people speaking different dialects. Once you decide on one then try using a lot of the slang you hear from those particular people. It's really hard to do it if you're not from here, as I can just talk to friends or watch TV and hear them all.
Research is the key, basically.
Lana Drake her accent is British and I had to listen and read about it , I'm trying hard to learn the accents and scottish by watching Dr.who and sherlock
I have a British friend who always told me to not fake a British accent, because the British will know... There are different ways of speaking for older generations, and your place in society (class). If its a re-occurring character I might suggest writing out the basics of what you want them to say, and then have someone who is actually British, re-write that dialogue (or translate it) for you to something that sounds more natural to them.
Just my 2 cents. 
It's nice that Hollywood is starting to actually hire British actors to play British roles, so Americans aren't faking it. 
Yeah, this is the problem. We have finely tuned sensors for non-British accents. I don't know about other accents but as soon as somebody turns up in a film, pretending to be a Brit, klaxons go off and my brain feels itchy.
The only one in my whole life who I haven't immediately sussed out is James Marsters from Buffy.
And then you have to remember all the "Afrikaans" accents or "Dutch"/"Netherlands" accents they try to fake as well... it sounds so horrible!!! Especially to me who is Afrikaans speaking!!! I want to laugh so bad!!! One actor I really feel doesn't make me embarrassed to hear speaking English with an Afrikaans accent is Arnold Vosloo (A South African XD) But he almost always plays the bad-guy roles!!!
Like why!!!!!! Why does the South African "outjie" have to be the evil villain???? Nooooooo!!!!!!!!!!
Most South Africans who are Afrikaans speaking today though have a fairly normal accent so they can really lay low on the effort, it's the older grandpas and uncles who think they are "oh so smart" that have these weird accents - only when they speak English - and the worst part about Hollywood movies are when they try to pronounce Afrikaans words...
A simple idea would be "Boerwors" they'd say it like "boo-e-force" when it should be closer to "Bo-r-a-v-o-r-s"
(Sound out each sound of the letter the "a" though more silent than the "a" for "a Cat")
So I think the same with Sticking to a British Accent try to understand in a written way would be to understand where certain "accents" are placed on certain words and find a way to so that in the written form;
Example:
Normal English VS a (my version) Scottish/Irish English (For the Divide United)
You - Ye
Mine - Me
They are hooligans - them hooligans
Those are just some quick ideas.
I'd avoid writing things out phonetically and stick with slang (like "innit" as someone suggested above). Slang over the United Kingdom will differ slightly from region to region, but I believe most of it is shared. Having someone refer to people as "lass" or "lad" can help, and perhaps you can have another character (who isn't from the same region) comment on the strangeness of their accent? It could clue the readers in without alienating any British readers, or making the dialogue less immersive.
Here is a list I words british slang
British slang list (click me)15
First, off when writing any characters its easier to write in the language you're used to, then in an accent. If you want them to have a accent just put a side note for them on the script. Then after you finish writing the rough draft of the script just replaced some of the words that could be british words/slang.
However, what's probably better is just watching a few youtube videos on making the character believable. Your character might be British but if you're from Britain yourself you might believe it is Amercian version/stereotyping the character as British.
Stereotyping if isn't used in "humor" then your work will be criticized and most likely you will have angry + this tigger me types of people that will come after your works on the internet and maybe in real life too.
Unless, your writing Hetalia then by all means go ahead and stereotype away.
Here is a youtube link to write characters that are believable.
Youtube video2
