Even if they were not short-staffed, the Planning Department will not take enforcement action on this because of the risk of losing on appeal, and the cost implications.
The only issue is the 20cm distance to the edge of the tiles, where the builders have sneakily built the eaves 'out' to gain that 20cm. You know it, the planning department knows it, the builder knows it, and we know it - but that's not sufficient in law. For all anybody knows, the eaves could have been built like that originally, in which case the dormer would then be pd, and the council would not be able to provide irrefutible evidence to the contrary.
That's why nothing will be done.