Parenting - behaviour/tantrums

[Brillit]

Please I am new to this site (1st day) so I am most probably repeating an age old "problem/challenge"
My nickname is Brillit or B
I have a 4.5 yr old son (only child) who has just started Primary school (reception).
He loved his nursery and we had very little problems of him not wanting to attend.
He has started to "push the boat out" which is not a bad thing (very tireing of course) however we seem to always end up in a stand off. He begins to hit me (and mum), says nasty things about us, refuses to do things when asked nicely (several times) etc.
Typical discussion would be:
B (me): Please go and get undressed.
S: Just a minute after this program.
B: It is time now to get undressed
S: In 5 mins.
B: No now please.
S: In 5 mins please.
B: No - if you don't I will have to take you upstairs and I know you don't like that etc.
It ends up being a stand off with me in a rage and he is in tears.
I am not sure what this is all about - I am always reasoning with him and at times it seems ok but then on other day it is hell!
I am not sure if it works but has any one got any suggestions of Golden rules about the house.
I am worried that it may also be related to a lack of self confidence/ esteem... could it be?
Thank you for your thoughts.
Brillit

oh lord sounds horribly familiar! Both my 2 have gone through/are going through this phase and I was only trying to remember this morning what I did about it with dd1. I found reward charts and postives work better than threats & shouting (plenty of those btw too). No reasoning with a 4 year old in my experience, it confuses them. Tell them how it is (but have built in get out clauses ready before you start so you look like you are meeting them half way). I don't think it is in any way related to low self esteem. I think it is related to being 4.
I personally have a zero tolerance policy with hitting and react very strongly to it. Time out in the bedroom, and clear sanctions (no TV for example) but making sure that they know this is a very serious matter and why.
Don't forget you are in charge of the TV. I make sure mine are dressed and breakfasted in the morning before TV is even suggested.
Good luck, it's damn hard but we are all in the same boat.