With all due respect Alexander, that's one of your more bizarre suggestions, given the relative sizes of that feather and a lesser spotted woodpecker (c.15 cm total length) - this is a feather from a much larger bird. That said, I'm not entirely sure which bird - it looks familiar (common buzzard perhaps, or the underwing greater coverts of a juvenile osprey?), but the uneven/offset barring pattern is puzzling me. It's not a main flight feather (see the even width of the vane on either side of the shaft and downy base), so it's most likely a covert, scapular or axillary (though it seems long in relation to its width for a typical covert). Though worn, the apparent soft edges and uneven pattern make me think of an owl, of which short-eared owl would be the best fit, but I'm not fully convinced by this either.
In short, if I were forced to guess I'd probably go for short-eared owl, but I'm really not sure and I feel like I'm missing something obvious...