It always pisses me off that they send tax credits bumph for last year and current year at the same time but in 2 separate envelopes so costing twice as much (to us taxpayers in the end) in postage as well as wasting paper (not just the envelope but they send a copy of the substantial 'Understanding your Tax Credits' booklet with each).
This year they've trumped themselves by sending out a reminder that I haven't returned my declaration at the same time they send the declaration form!