No there is no traffic management or throttling. Any issues are usually local to your area i.e. you may have a number of users in your area torrenting 24/7 causing the slowdown.
You have to remember you do not have a 1 to 1 ratio with broadband, you effectively share one pipe with a tonne of people.
In regards to the slowdowns though, the most likely cause is WiFI. During an evening the neighbours come home, connect to their WiFi, fire up various wireless devices and it affects the speeds you get. Have you verified with a wired connection?
My WiFi speed slowed down drastically when next door arrived with a family of 6 and stuck their router on the same channel as mine. Every evening it would half the speed I got.
Again WiFI is a shared medium. Having multiple houses close together, all using WiFi at once, often on the same WiFI channel may cause slowdown.
Edited by ukhardy07 (Sat 31-Jan-15 00:06:56)