How many laptops can I take from India to UK in flight?

The part in "Taking personal effects that you need for the duration of your trip across the border" in @Relaxed 's answer is not sourced (and it's clearly written from memory as we will see because the official wording is different) and it really needs to be because it's really hard to find. For example, the Travelling to the UK leaflet doesn't contain anything about it -- that leaflet only mentions the duty free limit which is not relevant for our case. Similarly, starting from the Entering the UK page you won't easily find these regulations.

But a little digging finds Notice 3: bringing your belongings and private motor vehicle to the UK from outside the EC says

You can claim TI relief for personal effects reasonably required for a journey such as clothing, toiletries, personal jewellery and other articles clearly of a personal nature including pets. An illustrative list of eligible goods is given in our Notice 200 Temporary Importations. You can claim relief for your period of stay in the EC up to a maximum of 24 months."

Notice 200 4.3 is

Travellers personal effects reasonably required for a journey

And in "Conditions of relief" we find:

Applicants must be travellers who are not normally resident in the EU

But I have not found an "illustrative goods" in Notice 200. I continued with the referred "Commission Regulation 2454/93 Articles 232(1)(a), 236(A)(1) and 563" at http://ec.europa.eu/taxation_customs/resources/documents/customs/procedural_aspects/general/regulation_2454_93_en.pdf but there's nothing further. (Probably for the better, what a nightmare would it be if the EU declared in 1993 what's reasonable and would need to update it every single time a new technical innovation comes to market!)

We can conclude that the original question is not answered in law and will be up to the customs officer to interpret whether two laptops are 'reasonably required". Since you can give a reasonable explanation this is likely.

In my original answer, I have mentioned that I crossed the customs borders of Canada, USA, UK, EU countless times with two (sometimes even three) laptops and noone bat an eye.