Quick back story. We're both late 20's, no kids, not married, and pay the min rent possible for where we are. (The City)
So my partner will very soon received a promotion which includes a pay rise of at least 40K. So far the dynamics of our relationship has always been 50/50 He does earn a bit more than me currently, but i've always been happy to spilt evenly. The new pay rise will mean he will be earning at least 50K more than me.
Our current salaries earns us OK money. We do save, but saving is slow because we aren't often left with much at the end of the month. I do want to progress and earn more, which i'm working on, but unclear on when this could happen.
What i'm asking is, would it be incredibly cheeky of me to ask that when he starts his new role, could he contribute more towards the rent? So 30/70? I will have an extra £200 a month disposable this way. This allows me to save more money for the things that matter (personal financial security, our future, etc) and create a more fairer structure so that we are both happy. (well, me anyway) 
I understand that he should be able to enjoy the money he makes with his promotion, after all, his hard work has created this opportunity for him. Perhaps i'm being selfish?
His promotion happened very quickly, we haven't had a financial conversation about it yet. I am unsure of how I can approach it in the correct way. We are sensible with money, no worrying debts or excessive spending.
What would you do in this position?