This is what I found on the net concerning your country....
My employer has introduced rules regarding taking deductions from my wages. What does the law say here?
A
All workers have the right not to have unlawful deductions made from their wages. For deductions to be lawful, they must either be required or authorised by legislation, or authorised by the workers contract of employment so long as a copy of the relevant term or a written explanation of the term is issued to the worker prior to the deduction being made, or agreed to by the worker in writing prior to the deduction being made. Further protections are afforded to workers in retail employment where deductions are due to cash shortages or stock deficiencies connected with retail transactions.
A worker who believes an unlawful deduction has been made may claim to the industrial tribunal assuming the internal grievance procedure has failed, and, if the claim is upheld, the tribunal can order the employer to repay the amount unlawfully deducted. If you complain in good faith about a deduction, whether or not the deduction was properly made, and you are dismissed, the dismissal is automatically unfair.
The Agencys officers should be able to assist you in other wage-related issues such as: national minimum wage, arrangements regarding stakeholder pensions and so on. Further information on deductions from wages is available from the Agencys Information Note 7 which can be downloaded from here
Information Note -
Deductions from wages by employers
If our answer or publications do not provide you with enough information please contact the Agency's Head Office: 028 9032 1442 - or our Regional Office: 028 7126 9639.
It appears to me, that your employer is in the wrong and have no right to take that money from you.
I dealt with almost this exact same thing a few years back and took my complaint to the Labour standards office and was given all my money back.