Answer
Respected Brother-in-Islam
Assalaamu Alaykum Wa Rahmatullaahi Wa Barakaatuhu
With regard to pants and shirt, this mode of dressing has not been adopted by the learned and god-fearing, hence, attiring oneself in this fashion is not desirable. Moreover, a person would be deprived of the reward he would attain by adopting the Sunnah mode of attire. (Fataawa Mahmoodiyyah, vol.17 pg.349; Mahmoodiyyah)
The necktie, however, is surrounded by a controversy concerning its origins. If it was really a part of Christian religious dress, as argued by some, then its use would be totally Haraam / prohibited, otherwise Makrooh (reprehensible).
and Allah Ta’ala Knows Best
Mufti Ebrahim Desai