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This came up recently actually, and if you search for old elderly you might find the thread.
Certainly "See that elderly gentleman over there? That's Sarah's grandfather" is more polite than "See that old guy?" Yet, when referring to someone as "elderly" you do give the impression the person is quite old, possible frail, etc. "See that older fellow?" is a more neutral (and perhaps more accurate, is Sarah's grandfather isn't in his dotage).
You've asked an interesting question. After it came up the other day, I asked my 80-year-old father what he though. He's content knowing that he's "old" but doesn't want to be referred to as "an old guy." He doesn't want to think of himself as "elderly" which sound even older than he is.
I think for your purpose, I'd use "older workers" and not try to use "old workers" (it does sound rude) and "elderly workers" (which makes it sounds like we're lucky they don't collapse from frailty on the job).
Sorry, I just saw you wanted BrE. This is an AmE point of view.