I asked the question in the Manchester Mac Store
I asked the guy in the Manchester Mac Store how to clean my screen. He showed me a cleaning kit they sell for £29.99.
He then took me to one side and said use some watered down windex and a decent microfiber cloth (He told me Tesco are selling a pack of 3 for 99p).
I did tell him I had a glossy screen MBP so not sure if same instructions for matt screen.