Miner or gall?

Miner or gall?

Observation - Miner or gall? - UK and Ireland. Description: Could be a holly leaf miner or a leaf gall - I haven't got the hang of distinguishing between them so any comments or confirmations are appreciated.

Could be a holly leaf miner or a leaf gall - I haven't got the hang of distinguishing between them so any comments or confirmations are appreciated.