https://glebekitchen.com/chicken-biryani-indian-restaurant-s...
Yes, about half the page is "story" but it's actually got some quite important information about technique, it's not all waffle about the author's grandmother's favourite cake plates.
Everything on that site is good. Read up on "British Indian Restaurant Technique" and you'll nail all your favourite curries first time - the garlic ginger paste and onion gravy are essential.
In London, the most authentic biryani (by which I mean closest to the original style, before other regions adapted it to their own tastes) is Awadhi/Lucknowi biryani. You can find a great version at Biryani Kebab & Chai in Soho, and another solid option is at TH@51 Restaurant & Bar at St. James’ Court, which is owned by Taj Hotels ,.. a very old school Indian hotel group ...