Imagining what it means to become a "redundant" employee, an American worker is likely to think of "redundancy" as the condition of having too many people doing his or her job, which means a risk of being laid off. However, in the UK, it does mean being laid off-precisely because of being a superfluous worker.

Hence in the UK, a redundant worker is not merely one who may be laid off as an unnecessary worker, but one who is being laid off for that reason. The difference between the circumstances of the American vs. the UK worker is that the American worker is left with anxiety in virtue of being redundant, while the UK worker is left with the prospect of possible unemployment benefits.
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"Redundancy", in American English designates the state of being superfluous, unnecessary or "supernumerary". However, in the U.K. it refers to being laid off in virtue of being redundant in the American sense, i.e., becomes superfluous and therefore applies when an employee is released from employment because (s)he is no longer required to meet the employer's needs.
The U.K. ERA 1996 s.139 states:

"For the purposes of this Act, an employee who is dismissed shall be taken to be dismissed by reason of redundancy if the dismissal is attributable wholly or mainly to
(A) the fact that his employer has ceased, or intends to cease
(1) to carry on the business for the purposes of which the employee was employed by him, or
(2) to carry on that business in the place where the employee was so employed,


(B) the fact that the requirements of that business
(1) for employees to carry out work of a particular kind, or
(2) for employees to carry out work of a particular kind in the place where the employee was employed by the employer have ceased or diminished or are expected to cease or diminish".

There are two types, voluntary and compulsory. The voluntary is virtually self- explanatory; where an employer finds they need to remove a number of an employees from a department and asks for volunteers to become redundant. Compulsory redundancy means that the management selects the group to be released, usually keeping those employees with higher skills, qualifications and overall work performance.

Those employees who are let go qualify for "redundancy pay", which is subject to many of the rules of unemployment benefits, e.g., the employee must have been with the original company for a certain amount of time, must have made a certain income and termination must have been classified as "redundant".

All the information needed to be eligible is written up in the contract signed at the time of the start of employment, so the employee knows what is available to him/her should it happen.