Help writing formal inquiry letter to potential new employer

Hi, could someone help me out with writing a formal inquiry
letter to my potential new employer? I have been extended verbal job offer, but lack of written confirmation has made me very anxious and I'm worried that I will sound bit frustrated. Besides, I am not a native English speaker and have this tendency to be overly straightforward. I just don't want to say something inappropriate like do you still want to hire me?? I have exchanged some emails with them, and was told they would get back to me once the executive is back in the office and they discuss it with him. The problem is they haven't said when would that be! So now I'm in Limbo, not sure whether i have a job. This is what I have for time being, would appreciate if someone could check and correct if for me.

Dear XXX,

I know that you said you would get back to me once you get chance to discuss the situation but you haven't really specified when would that be. I have accepted your offer but have nothing in writing and it is a bit of concern for me. Please advise whether you would be able to confirm anything by the end of the week, even a general estimate of when would you anticipate me to start the position would be good. I just need to know for planning purposes.
Regards,
M

PS Sorry for re-posting, but i did previous post as an anonymous and I wanted to be informed if it gets answered