This popular vegetarian restaurant was opened in 1994 by Das Sreedharan, who had come from Kerala, India, to study in London. Dissatisfied with the quality of Indian food in London, he wanted to bring the authenticity of Keralan home-cooking to the city. The result is a menu steeped in the flavours of the region, with an abundance of dishes to choose from. Vegan and gluten-free options are available, as are dishes free from onion and garlic.

There are pickles, chutneys and pre-meal snacks to begin with: poppadoms, banana chips and crunchy seed sticks. Then starters such as lentil cakes, fried plantains and a selection of savoury street snacks popular in South India.

The mains are split into dosas and curries. Dosas, a type of crispy pancake made of rice flour and stuffed with vegetables, come in different styles with fillings such as potatoes, beetroot or onion. The menu lists almost a dozen curries: from tangy tomato dishes to spicy aubergine to paneer and spinach. To compliment the mains there’s a range of rice dishes, side dishes, soups and breads. And to follow, a choice of sweet treats – many of which are made with fruit and flavoured with cashews and raisins.

The ‘Kerala Feast’ is a great option if you’re tempted by more than one dish. At £17 a person, it samples from the entire menu: it really is a feast.

There’s a lively yet relaxed atmosphere in the restaurant. Due to its relatively small size, the tables are set fairly close together, but the music volume is low and acoustics are good, so conversations feel intimate. The service is friendly and attentive, and the staff are happy to recommend dishes based on your likes or dietary requirements.

There’s now a chain of Rasa restaurants in London and India that, unlike Rasa N16, serve omnivorous options as well as vegetarian food (one of which, Rasa Travancore, sits across the street). But Rasa N16 was the first of them and, for veggies and vegans, it remains the best.

Inside, tables for two or four sit beneath dimmed pendant lights, creating a cosy, if simple, interior. Near the back, a spiral staircase leads upstairs to more seating. Enclaves in the wall house small statues and icons, and several gold-coloured textiles hang from the wood-panelled walls. If the surroundings are modest, the menu is a blazing contrast: a wide-ranging list of over 50 individual options.

To start, there are South Indian specialities such as: vada, a serving of lentil donuts soaked in warm soup or served on their own; samosas; and rice dumplings with spices, nuts and chutney. Along with other fried snacks and soups, you can find different types of puri, an unleavened bread served with vegetables or chutneys.

For mains, there’s a terrific choice of vegetable curries (over a dozen including bhindi bhaji, channa masala, saag paneer); thalis (huge platters of starters, sides, curries and desserts), and uttapams, a thick rice and lentil pancake similar to a dosa but topped, like a pizza, with vegetables and spices.

The dosa is perhaps Sagar’s signature offering; it’s stuffed with potato, onions and carrots, flavoured with different spices, and served with coconut chutney and soup. If you don’t mind upstaging those around you, try the impressive paper dosa, a table-sized crispy pancake.

Drinks-wise, you have the option of lassis (yoghurt and milk), soft drinks, vegan wine, beer and hot drinks. The dessert menu includes sweet puddings made with rice, raisins and nuts, and a selection of ice creams and sorbets.

Dishes on the menu are clearly labeled for allergies, and dedicated menus with lots of options are available for vegans and those wanting dishes free of onion and garlic. The standard menu doesn’t explicitly mention ghee (a dairy product), so ask your server if you’re unsure.

Its lively atmosphere, great food, and friendly, attentive staff, make Sagar the perfect spot for a relaxed lunch or dinner in central London, for tourists and Londoners alike.