Hello Jaya & all
https://www.compareholidaymoney.com/buy-currency/indian-rupees.php (there was, incidentally, no customs goods import check either: all I had to do was fill in a customs declaration form and then post it in a box at the airport!).
I was advised not to exchange money at the airports as the exchange rate was bad, so I exchanged Sterling at a bank next to my hotel in Delhi. This proved to be a wonderful introduction to Indian bureaucracy: no problems with Sterling per se, but it took well over half an hour to exchange GBP200 into INR, and involved the photocopying of my passport and the services of an astonishingly large number of people. The bank itself was a very interesting place: open plan, with each position having a large yellow card with the job description (in English and Hindi(?)) of the person sitting there and/or the function of the department located there - all preceded by a large yellow sign saying "May we help you?" (although the welcoming tone was dampened a little by an even larger yellow sign: "You are under surveillance")
There was an ATM outside the bank - but this reportedly did not work . . . . .
Two hundred pounds' worth of Rupees proved more than enough for two weeks, as everything I wanted was very cheap (and I am not a shopaholic) - any more expensive items could easily be purchased using credit cards, which seemed to be accepted everywhere I went.
The notes which I obtained were better than I expected, especially the larger denominations (INR100,500), which were like well-used £20 notes - but I soon acquired a large collection of filthy crumpled small-denomination notes (INR10, 20, 50), after the handling of which I definitely felt the need for some antibacterial hand gel. I found that in practice all restaurant bills were rounded up, so I never saw a coin until the last day in Mumbai, when I received two 1Rp coins with the exact change (in a 5-star hotel!) when I settled my hotel bar bill. I shall treasure these.
Jim
PS - there is a picture of the notes and coins on p.769 of the DK guide to India.