UPDATE: Hey, guys! I thought I'd just post a quick update as to how I've fared since posting this thread. I'm happy to say that I've now watched 4 movies without a single freeze!
After posting this thread I sent Sony an email regarding my situation and how I could possibly resolve the problem. Sony were quick with a reply which contained two helpful links to various probable solutions to the issues I was having. One of the things Sony told me to do was to go to 'Video Settings' scroll down to '1080p 24 Hz Output (HDMI)' and switch it to 'Off'. Later that night I watched a movie and it didn't freeze. I didn't get too excited as this was the symptoms it had been showing, one movie freezes, the other doesn't.
During the next couple of days I gave the PS3 a good sucking out with a hoover, and finally, I bought a Blu-ray lens cleaner. Since then I've watched three movies without a hiccup. Fingers crossed, but it looks like the problem has been resolved.
I just thought I'd post this in case anyone ever has the same problem one day.
