Why is Tilda basmati rice so popular?
I don’t know to what degree things have changed over the years, but according to this article from The Independent in 2000 there is a lot of fraud in the rice business, with Patna or hybrid rices being passed off as Basmati.

Just as fraudulent dealers bulk up Darjeeling tea with inferior leaves, for some time now unscrupulous traders have been passing off inferior grain as basmati or adulterating it.
I contacted the Rice Association, a branch of the Food &amp; Drink Federation, to hear that the Ministry of Agriculture exposed the scam over a year ago. Samples of 41 basmati rices were sent to Nottingham University, where the DNA &quot;fingerprints&quot; were compared with those of authentic basmati. No fewer then 19 samples were found to be adulterated.

Tilda have closer control over their supply chain than many other suppliers and, in testing, were not found to have substitute rice varieties being mis-sold.

Tilda, a leading rice importer which buys direct from the Punjab through its own agents, was responsible for seven of the 22 authentic basmatis in the test.