Ah, that explains it. Tikki/Tikka Masala isn't really an Indian dish at all:
"Chicken Tikka Massala is now a true British national dish, not only
because it is the most popular, but because it is a perfect
illustration of the way Britain absorbs and adapts external influences.
Chicken Tikka is an Indian dish. The Massala sauce was added to satisfy
the desire of British people to have their meat served in gravy. "
- Extract from a speech by British Foreign Secretary, Robin Cook.