Normal Tax code

Hi all

A client has brought in his payslips for completing his tax return. He worked in the film industry (but is not a performer himself) and had taken 3 different employments during the year. The monthly pay are different in each month, possibly based on the no. of hours worked during the month.  It seems that on each of the employment he suffered between 23% and 28% tax (excluding NI) although the payslips show normal tax code. The overall income is about £45k and total tax suffered is 27.5%. Any ideas why he may have suffered so much tax.

Thanks for any suggestions.