Firstly I would like to express my gratitude to everybody who took the time to try and help a numpty like me with this problem - Thanks guys!!
Secondly (and I can't believe it was this simple!!) it would seem that DiscoSteve came up with the correct answer. I was using a mouse mat but I changed it over for a cheap 85p one from Wilko's and hey presto no further problems.
Thanks once again fellas as it is was driving me up the wall.