If you visit these coordinates, you should be standing near a bus stop called 'Hall View': this is named after the road opposite and refers to a grand view you would get of Eltham College had the houses not been in the way.
This cache will be easy for those with a mathematical backgound...
For the northings:
f(x) = 4x + 5 g(x) = 3x - 9 h(x) = 5x - 6
Work out hfhf(3) - 2 x fgfg(7) - 14 x ggg(5) + 6. You should get a three-digit number, abc.
For the eastings:
f(x) = 2x^2 + 5 g(x) = 2x - 4
Work out fggfg(3) = answer 2
f(x) = 2x^2 - 16 h(x) = 5x + 5
Work out hfhf(3) = answer 3
Then do (answer 2 - answer 3)/2 - 12. You should also get a three-digit number, xyz.
Assuming N51 26.abc and E00 2.xyz, you need to add the correct information to trigger the solution checker.
Visit these coordinates and you should see the cache host: I'll call him Harry.
Good luck!
Congratulations to HouseOfDragons and Idreamer for being FTF!