Hello,
difficult for me too. But its a Serin imo:
- head pattern is good for a Serin for me too, including very narrow supercilium and just guessable yellow forehead
- I am not so sure about colour tones: yellow seems good for Serin, and yes, within variation for a Cirl Bunting. But many are warmer, creamer or more buffish-orangey than your bird
- taken all pictures together, bill seems stubby
- yes, "tramline" pattern on the back with much grey between dark tramlines seems much better for Bunting than for a Serin for me too. (So I skip this. Advisable?)
- I have seen Serins with similar pale grey backs without any colour tinge (at least in the field) before, but I havent found a picture online during a quick search
- my impression is, that the parallel, narrow and whitish wingbars are better for a Serin
- the appearant full and broad tail is an artefact imo, just bad placed vegetation???
Conclusion? After looking at your pictures, its still a hard one for me (can I blame picture quality??? I hope so), but like you, your bird seems to have a convincing Serin head (and a stubby bill?), so I think its a Serin as said.
I assume, that you havent more pictures?