The easiest way to travel to the UK from India is via air travel. There are numerous flights that fly daily from all major international airports in India to all major cities in Europe such as Paris, Berlin, London, Frankfurt and Amsterdam among many others. Numerous flight options are varying in price and travel time. Unlike other popular tourist destinations such as USA, Canada or Australia, you can get direct flights if you choose the carries of the country you wish to travel too. All major European airlines offer multiple flights to Europe form major India cities such as Delhi, Mumbai, Chennai, Kolkata, Hyderabad and many more. You can book direct flights or do a break journey of you wish to fly to travel to multiple destinations.
In term of cost and time its best to fly to London from Delhi, however, if you don't live in Delhi there are many options from other major cities in Indian, and you can choose the best option for yourself. You can even get direct flights to London. However, they cost 20-25% more although you can save a few hours each way.
Frequent flight names: Air India, British Airways, Singapore Airlines, Air Italia, etc
Biggest airport: Heathrow Airport