Hi sapphire9, I don't think you can check more than 180 days worth of results online. You would have to phone them up and take the details (if you just want one nights numbers) or write to them and ask for a written copy. The phone number is on the back of the play slips.
National Lottery Line 0845 9 100 0000
I've spoken to them in the past, and they are very helpful.