Here is a list that you might find useful. I am not certain about every single term on the list, but most of it strikes me as sound. Perhaps one of native speakers of BE here can point out if there is something amiss, but it should cover general terms sufficiently.
But in general I wouldn't worry too much. For one, Lara Crift is a globetrotter. She's been around the world a couple times. She might as well have picked up a smattering of slang and idiom here and there and mix and match it freely. To show off her upbringing I would focus more on perhaps a somewhat refined manner of speaking and less on terms or spelling, i.e. not using colloquialisms in certain situations, sometimes writing "it is" instead of "it's", and so on.
That said, from my experience, attempts at writing certain speech patterns end up being either too subtle to be widely noticed or too strong to feel real, most of the time.
A modern, young British royal who has travelled and fits in is Prince Harry, who has the public school accent not a London accent. I used to know a Lord who speaks rather like Harry and have met one who was of his father's generation.
Harry would probably say "Half past ten" his father's generation telling the time would probably sound a more clipped "huf pust ten"
Keeley Hawes voiced Lara 2006 - 2013 so may give a good guide.
Frequent usage Dictionary English American English
crisp potato crisp potato chip
silencer (on a car or gun) muffler
tube underground subway
Vet veterinary surgeon veterinarian
Carriage wagon (on a train) car
Generally, if pointing out something "It is plain to see." would be used losing patience formally with an official of some sort in a dispute. Amongst friends "It's obvious." Being sarcastic "Plain as the nose on your face." The accent stays the same but the choice of words can alter.
I was raised to speak BBC English there was a Scottish influence but I rarely use a Scots word like wee for small.
I hope that helps,