It would depend on what you mean by "without your permission" and "£8000 bond outstanding"? If the contractual terms of that "bond" allowed your friends employer to make this deduction, and if your friend agreed to it, then section 13.1 of the Employment Rights Act 1996 would seem to have been complied with.
Section 13. Right not to suffer unauthorised deductions.
(1)An employer shall not make a deduction from wages of a worker employed by him unless,
(a)the deduction is required or authorised to be made by virtue of a statutory provision or a relevant provision of the worker’s contract,
or
(b)the worker has previously signified in writing his agreement or consent to the making of the deduction.
Reference
Some of the comments above are wishful thinking and nonsense.