Marmelade at teatime - I think not 
Silver. Buys your own silver.
Even worse - have fish knives
To my mind, the difference is the duration and the hazard:
A prat is annoying and self-centered but harmless, and may just be behaving badly. The worst he will do is brag about something and, when challenged, turn out to possibly be right (costing you a round of drinks or a tenner). Jerk, wanker, braggart, and bore are all near-synonyms. People become prats when drunk.
A twit is someone who is not just thick, but possibly stupid in a way which could harm others, and is not likely to change. Bad drivers or people who stop at the tops of escalators are twits. Junior military officers are often portrayed as twits because they have the power of life and death over their men but lack the experience or knowledge to use it well. Upper class folks – especially politicians who make decisions that affect us little folks – have so much power that even a little stupidity is dangerous and are often lampooned as twits. Fool and idiot are okay synonyms, but from context, I always got the impression that a twit is a fool or an idiot whose actions are hurting others.
This is exactly how the guy I mentioned from The Apprentice came over. As one newspaper reviewer commented “you wonder how he survived on the streets of Basra for six minute, never mind six months”. Military life could not have suited him, because he is still in his 20’s, and had left the army after serving as a junior officer for just a few years.