Solved Help to identify hedges please part 2

Silver Surfer is correct in everything. If the ash is inside the hedge, as it appears to be, you can only cut it to the ground. I doubt that it was an intentional planting in the mixed hedge but is probably self seeded.

The trees in the hedge will get cut as normal when cutting/shaping the hedge. If any are particularly vigorous growers and suddenly shoot up higher, or outwards, then you just cut them off at the same level as the hedge each time. This is just part of normal gardening and is a simple thing to maintain.