Uniform tax

Dazed_and_C0nfused

It's highly likely that you overpaid £10-11 in each of the first three (after factoring on the £1-£2 most people on PAYE underpay each year).

Same in the fourth year, so a total £40+ tax overpaid.  

But in the fourth year you underpaid a little because of the overlap in jobs (that's not an uncommon thing to happen) and the bet result is you have still overpaid but only £12.80 after taking into account the tax owed in the fourth and final year.