Things cheap in UK London comparing to India [closed]

If yes where these can be purchase?

The bulk of what you are looking for: mobiles, external hard drives, ear phones, power banks, and watch are sold all over London. But if you want to see lots of electronic stores in one district, invariably the answer is Tottenham Court Road.

The 'district' begins at the Tottenham Court Road Tube Station and extends north for roughly 1/2 km on either side. To help recognise it, here's a screen cap from Google maps...

You asked about price. The close proximity of these shops forces them to be sharply competitive. And moreover, there is an unspoken 'ethos' that all prices are the 'starting price' and subject to negotiation. You asked about comparison to similar products in India. Many of the staff in these shops claim south Asian heritage and should be able to honestly quote you the differential (if there is one). They would also be able to signpost you to a reliable source of India's tax and custom regulations.

There is also an interesting College Computer Fair just off Tottenham Court Road near Goodge Street. It runs on the weekends, but always double check the College Computer Fair site for details.

Finally, some of the items in your shopping list were items of clothing. There are many cheap places, but the Petticoat Lane Market is legendary for it's prices and selection. Here's an image from the Wiki...

Source: Wiki entry for Petticoat Lane Market

The nearest tube stop is Aldgate East Station.