Is this a Warbler or a Juvenile Siskin (or other)?

Spotted this small newcomer on the Nyjer feeder this morning. Pictured with a female sparrow, for scale. The light in the photo isn't brilliant, but it had a definite greeny/yellow colouring that makes me think it isn't just a young sparrow. That and the eye marking / wing bar had me thinking Yellow Browed Warbler (although I know they're rare!), but on studying the photos it seems a lot streakier than a warbler. Is January the wrong time for a juvenile Siskin? Or am I way off base? 

For context, I'm in the suburbs of Glasgow, with a good bit of green space and conifers near the garden where this was taken, and less than a mile from a river with a small deciduous woodland. I've got suet balls, buggy nibbles, sunflower hearts and peanuts also on offer.