After living here for a few years, I've visited a few Portuguese restaurants to have that taste and smell of home. Well, not quite home, but it does come close enough.
First Portuguese restaurant I went was in Walthamstow. Can't remember the name, but that's not an issue because it was a bad experience. Not the best way to start my Portuguese experience in London.
Next, I've been to A bite in heaven. Always in a group, so we usually have a buffet service there. There's also karaoke in the evening, which can be quite a bit noisy. It's a small and cosy place, and the food and service are quite good. 'Bacalhau com natas' is a very nice dish that they serve here.
Another one is Casa Madeira. The restaurant is quite big, in Vauxhall, and not only you have the restaurant but you also have a Patisserie, which let me tell you, is quite good. All those Portuguese delicacies, very very nice :) There's also karaoke in the evenings, but because is a bigger space, is not so noisy and you can still have a relax meal with the music in the background. With big groups (40+) they tend to rush the food a bit, but otherwise is great quality, very tasty, with some traditional dishes from Madeira and the service is quite good too. Do try the 'Espetada Regional'
Next on the list is O Cantinho de Portugal. This is a medium size restaurant, usually packed on the weekend so either book in advance or arrive early. There's a bar so you can always wait there until a table is available. They focus more in food from the mainland, but again, service is quite good as is food. I personally recommend the 'Francesinhas'.
Another one I go with some regularity is A Lua. It's a very cosy place, with good service and the food is quite nice. Again they serve traditional food from Madeira. If you do go there, do try the 'Picado regional' and don't forget to ask to add mushrooms :)
Finally, the last one I've visited was O Barros. Went for a dinner there, without any recommendation, but was pleased with the food. It doesn't have live music, the restaurant area is small and cosy, service is good, and again, the food was delicious. Going there, do try the 'Cozido a Portuguesa'.