Thanks both, glad you were so positive that retirees is correct catron. Internet dictionaries suggest both as correct but I feel that retirers is just a sloppy word probably invented by our trans-atlantic cousins who use words like realty,honor and the like !!!
Sorry, manofsteel, should perhaps have said why I know that it is the correct answer. The Telegraph Crossword Society allows one to check answers - if they are right they are coloured green and if wrong they are coloured red. Retirees was coloured green and is therefore the correct answer - or the one that the compiler was looking for, at any rate!