TIME LIMIT WARNING
If you think you might want to take your employer to the Employment Tribunal, it is important to bear in mind that there are strict time limits. If you present your case to the tribunal late, it will almost certainly be rejected, unless there are exceptional circumstances to explain that failure.
The simplest rule of thumb is that you have three months less one day from the point your employer fails to pay you to start Early Conciliation — which is the first step before bringing a claim.
After ACAS notifies you that Early Conciliation has ended, you will have at least a month to present your claim to the Employment Tribunal (provided you started the ACAS process in time).
Example
John was supposed to be paid £1,800 on 1st February. Instead he was paid £1,500. John has to notify ACAS for Early Conciliation no later than 30th April. If Early Conciliation starts on the 30th April and ends on the 10th May, he then has until the 10th June to present his claim to the employment tribunal.
If there have been a series of deductions from your wages time starts running from the last in that series. So if the same deduction has been made for a number of months, time will run from the last month.