You're not barmy at all andy, it's a tricky balance to achieve. I can't tell you what BIR's do, but I can tell you what my method is and you may find it works for you.
Firstly, you need to select the waxy kind of potatoes and not the floury ones as floury potatoes tend to disintegrate if you overcook them. You can partly pre-cook these if you want to or cook them from raw, but you'll need to get the amount of liquid correct if you cook them from raw.
Secondly, I don't know what recipe you're using but I'll outline my method below and I'm deliberately not going to give you a recipe - but a technique.
1/ Heat some oil in a saucepan, I prefer a smallish saucepan for potatoes rather than a frying pan and add if using whatever whole spices and fry till fragrant.
2/ Add your onion/garlic/ginger puree and fry, then add your tomato puree if using then your spice mix and fry that.
3/ Add your potatoes, par-boiled or raw and chopped into equal sized pieces so they cook evenly and mix into the spice paste. Remember, the smaller the potato pieces the faster they'll cook.
4/ Now add your base gravy, boiling water or stock or whatever you use and bring to a boil.
5/ Now turn down to a simmer, cover and simmer for however long it takes for the potatoes to be cooked through. Somewhere around 30 mins should be about right depending on the size of the potatoes pieces.
6/ You may need to add more liquid if it becomes too dry before the potatoes are tender or you may need to take the lid off the pan and fast simmer for a few mins to evaporate any remaining liquid, just make sure the potatoes and spice paste doesn't stick to the bottom and burn.
The key to success here is to use waxy potatoes, not floury ones and to add just enough liquid to allow the potatoes to simmer for most of the time in liquid but for this to evaporate and end up with the spice mix paste to cling to the potatoes once they're cooked through. The final dish should be dryish with little liquid and with the spice paste clinging to the potatoes.
I then usually add a squeeze of lemon juice, some chopped coriander and a finely chopped green chilli or two.
Experiment with this method and work out what recipe works best for you.
Topic: How do you cook potatoes for bombay aloo? ( 4,143 )