The British national dish?

Do an internet search on the terms "british national dish" and nine times out of ten, the output will mention "chicken tikka masala". And by that, the reference means the top representative dish. Surely, it must be just one of the great British national dishes and the word in this context simply means "across the nation". Other notable British national dishes  would be fish and chips, the Sunday Roast, bangers and mash, pie  and mash, the full English/ Scottish breakfast, and high tea.

How is it that a dish of Indian origin has that high place in British food taste esteem? It seems that the dish was supposedly concocted in Britain by immigrant cooks from the sub-continent for the Indian (and Pakistani/Bangladeshi) restaurant trade there. Britain has had a long history with India and people had moved from the latter to settle in the "mother" country over many decades. They brought their food culture with them. Thus, all over the British Isles one would find good eating at sub-continental-themed restaurants. On my latest trip to Britain (at Edinburgh), I resolved to try the "national" dish.
 

Chicken Tikka Masala (£11.95)
Chaskaa Indian Restaurant
30 - 32 Leven Street
Edinburgh EH3 9LJ

I ordered the take-away rather than dining in as the space in the restaurant was rather small and enclosed (concern for COVID-19 risk). My side was a plain naan (£2.25). Not shown here was an accompaniment of a giant papadum.

It is said the tikka (it means "piece" or "chunk" in this usage) is always from chicken breast cuts. It is typically marinated, roasted and then drenched in a gravy (the " masala").

My impression? It is rather like tandoori chicken in a gravy. However, I think tandoori chicken might be better with masala because chicken breast pieces turn out dry whereas I would have gone for a hind quarter piece of chicken for this tikka dish (not normal). The masala itself was rather mild (not spicy). Overall, I am not sure why this dish is regarded so highly in the British Isles. I would prefer more traditional Indian fare.