A person can only be made redundant when his job no longer exists - irrespective of his excellent work record, or poor sick record.
Being off sick does not bar redundancy, nor is it a reason for making someone redundant.
The company must follow proper procedures during the redundancy process. Last in, first out is an acceptable method of selecting people for redundancy.
Good advice here:
http://www.direct.gov.uk/en/Employment/Employe es/RedundancyAndLeavingYourJob/index.htm