If you've worked for an employer long enough, you'll automatically be entitled to a certain amount of redundancy pay. (See link for details). Some employers pay more than the statutory minimum but they're not obliged to do so. In particular, some employers
might offer an incentive to those who volunteer for redundancy but, as stated, they're under no obligation to do so.
There's loads of information here:
http://www.direct.gov.uk/en/Employment/Redunda ncyAndLeavingYourJob/Redundancy/index.htm
Chris