If you absolutely MUST set a book in London, then for the love of everything that is holy at least visit the city. Or find a beta reader who is a Londoner.
Because I'm barely into the book and:
1) The heroine remarks with surprise that the London streets are crowded for a weeknight. Dear Raine, London streets are ALWAYS crowded. I have the bruises to prove it.
2) The hero buys the heroine Advil. Advil is not sold in the UK. (Editing to add: Before you feel the need to tell me I am wrong about the name of the drug, the sentence is: "He shoved a bottle of water into my hand and opened up a single packet of ADVIL." Loc. 154 on my Kindle. The original self-pubbed version of the book.)
3) The hero buys the heroine a Power Bar. But sports nutrition bars are nowhere near as ubiquitous in the UK as they are in the US.
4) The hero pulls into strip mall (!!!!) to buy the above items. No. No. NO. London is NOT Southern California, Raine, dear. In fact, I don't think there is a strip mall in the whole of the British Isles.
5) The hero drives a Range Rover. In London. This supposedly marks him as wealthy and sophisticated. Instead, it makes him stupid (the price of petrol in the UK is more than double the price of gas in the US) and for a security guy, not able to traverse very many London streets (they weren't exactly originally built for cars, much less Range Rovers.) Not to mention the problem of where to park it while out and about! Car parks are few and far between, and available street parking even more rare.
While some in London do drive SUVs, the vehicles are known as "Chelsea Tractors" and it's usually a trophy wife making a school run behind the wheel. Otherwise, the Rovers stay at the country house. Wealthy men in London drive sleek European sports cars or, more likely, they have a town car and driver.
Problematic setting aside, the writing is decent if badly in need of a good pruning by an editor. Spelling and grammar are, for the most part, acceptable. But the characters already grate.
Brynne appears to be TSTL. She accepts a ride home from a stranger, takes the pills he offers her, then falls asleep in his car. When she wakes up she freaks out - but it's not because gee, a stranger fed her pills and she passed out which YES IS CAUSE FOR ALARM. No, instead Brynne is freaked out because of some DEEP and MYSTERIOUS cause she can't think about. And then, of course, she wants to take off her clothes and roll around with the man she JUST MET despite freaking out in his car.
Brynne later castigates herself for being stupid. Gee, ya think? :rolleyes But that self-awareness comes too late to save her for me.
Ethan isn't much better; there's no way he's British, for one. Second, he's a friend of her father, yet he repays that friendship by buying nude portraits of his daughter. Then later, he acts surprised when he learns Brynne is American - but, dude, you know her father and it's implied the father is an American politician so, um...
Cannot read further. I have a low tolerance for festivals of stupidity.