Is there a quick and foolproof way of getting the reticle perfectly horizontal on the rifle without buggering around for 30 mins like I have just done?
It seemed to be off ever so minutely every time i nipped it up. In the end I'm not even sure I'm seeing it straight even if it is!
I use as many small spirit level inserts - courtesy of ebay - as I can fit on the stock to make sure the rifle is level, and look through the scope at the brick wall of the house opposite.
I work on the assumption that the builder has laid the bricks straight (!!?), so the horizontal gap between the bricks is a good guide to make sure the reticle is level.
A common mistake that people make when trying to design something completely foolproof is to underestimate the ingenuity of complete fools!!
Douglas Adams, 1952-2001 RIP
Mount the scope in the rings so it's held firmly, but you can still rotate it. Get the eye relief correct.
Using a straight a line on the floor like a floorboard or tile edge, line the toe and heel of the rifle butt along the line. Then look downwards, the wrong way through the scope . . . you should be able to see the line on the floor super-imposed with the scope reticule. Rotate the scope until the two line up and tighten the scope rings. Job done.
way of getting the reticle perfectly horizontal on the rifle without buggering around for 30 mins like I have just done?
Or get a Spuhr mount with a built in spirit level and comes with a wedge to level the scope 
Expensive yes but you only buy once 