Low helis
We get military overflights en-route to and from Otterburn Ranges. (We are also on the approach to EGNT R07, so they cross above the Curry House.) On one occasion a Chinook was VERY low (so low it lifted the leaves in the garden!). I contacted the Low Flying hotline and received the reply that by their nature, helicopter flights were 'cleared down to ground level' and there were no minima (as there are with fixed-wing a/c).
BTW I wasn't complaining, merely being curious. As far as the fixed-wings are concerned I say the lower the better (though at very low altitude they pass too quickly to identify!).