Conversation:

I'm originally from the north-west of England where the 2 legged garments are known as "pants". Even "long pants" and "short pants".

I once confused a southern colleague by telling him I was going out in town on a Friday night in "just pants and a shirt".

You are right(reader from the north-west). Many parts of England do NOT commonly use the word ‘trousers’ and do NOT use the word ‘pants’ for underpants.
Where I come from (the north-east) and I daresay many other parts of UK we normally use ‘pants’ for trousers and ‘undergarments are called ‘underpants’. (We do use sometimes the word ‘trousers’ but not normally.)It is so arrogant and so typical of many from the south of England to presume to speak for the WHOLE of England. Will they ever stop doing this?