A Puzzle-style Letterbox/Hybrid not hidden at the given co-ords. Instead, you have to imagine you're firing a cannonball into the woods from that spot. You aim 163° 29′ 16″ (not magnetic) and Fire! The ball leaves the barrel - which you can assume is at the same elevation as the landing spot - at a hefty 136.1m per second (304 miles per hour!). The launch angle is 20 degrees. Luckily wind speed and direction perfectly counteract the effects of air resistance and Coriolis force and you can assume Ashridge has acceleration due to gravity of 9.80665 m/s2 or 'standard Earth gravity': g0. Therefor the ball would land at the standard, parabolic theoretical position. And that's where you'll find the cache!
If you're lucky enough to remember your physics lessons you should have no problem(!) but if the maths of ballistics isn't so familiar, you will need to research the subject online. Your GPSr or Geocaching App may have a sufficiently precise 'project a bearing' function, once you have a distance which you could use to calculate the landing point/Cache location. If not, you will need to do some trigonometry or find help online. Various sites and methods may give slightly different answers, based on various assumptions (such as using a 'Flat Earth' model), but there's a good clue to get you to the cache, and extra info below. So, where's the cache?
Remember:
You cache at your own risk, but the cache isn't anywhere risky.
The cache is within 1 mile or 1.6 Km of the icon, but not at/close to the icon.
The cache isn't hidden within 0.1miles or 161m of another cache.
The cache is beyond a road. Please cross with care on a footpath.
The cache isn't hidden anywhere private.
There is 24-hour/year-round access to the cache.
The cache is in a public place; please hunt discreetly.
Please DO NOT remove the stamp or ink pad. Neither is a swap - They make this cache a LetterBox/Hybrid. Thank you!