Sometimes in your first year at a new job, the PAYE coding used is what's known as "emergency coding". This code ensures you are not underpaid on your PAYE. It does so by assuming you worked the first part of the year and thus withholding more (since more of your income is presumed to be in the top tax band). The upshot is you have over-withheld and are due a refund. Then again, some bookkeepers are far more capable than others and the PAYE coding could be right from the get-go. You thus have a good probability of a refund for 2006.
In your final year, something similar occurs. The withholding up until your final paycheque is done as if you will be working there all year. That last paycheque will either have the PAYE adjusted correctly for having left your job, or you'll have a clue-less bookkeeper who withholds the same amount as usual. This happens less often, but still happens often enough to be worth checking out.
Remember, a system is only as good as the people who operate it. You know what a Gaussian bell curve looks like; most bookkeepers are merely average and there will always be the 10% who aren't as good as the remaining 90%. If on the other hand your employer is blessed with one of those rare bookkeepers who fall into the top 10%, your PAYE withholding will have been correct in both the first and last years.