I've been going to the Banana Leaf restaurant for around five years. I've tried (I think) nearly all of the South Indian restaurants around London and I can honestly say that this restaurant is in my view the best. My girlfriend and I live on the other side of London and we happily make the journey approximately once per month to enjoy the high quality authentic cuisine they offer.
The staff treat you like royalty, the owner is a wonderful friendly lady, and very caring towards her customers.
The menu offers a wide and delicious variety of South Indian dishes ranging from mild to quite spicy with superb vegetarian as well as meat dishes - something for everyone.
If you're not averse to green chillies, try their Dry Sizzling Chilli Paneer with rice and dahl - it's truly one of the best examples of it's type I've tried in the UK.