Good advice above, I would add take your time deciding, the scope in my opinion is more important than the rifle and there is nothing you can do to change the scope...most rifles can be fettled to be very accurate out to 45 yards and made to fit the shooter - hard to fettle a scope

It has taken me over a year to get beded in with my current scope, I can now range very effectively with it, its all too easy to keep chopping and changing scopes - don't do it, learn the one you choose.

On actual specification these are my preferences but many in HFT would say the exact opposite.... - the best quality lenses you can afford, as said small objective (gives better depth of field), fine reticle (but not too fine such that its lost on dark targets), plenty of meaningful aim points for elevation and windage, low profile covered or lockable turrets, compact, lightweight, robust.....

You will find as many who like larger objectives, thick plain reticles....scopes are very personal.

On the 12x, I have heard this quoted as a maximum before but never seen it written in rules......urban myth maybe.... its not in UKAHFT, I can see you are in Southampton, just had a quick look at Central Southern rules cannot see their either?

Most shoot at 10x magnification, have seen some shoot 8x or 9x, rarely see higher.....if you want to bracket for range 10x is true Mil on most Mil type reticles.

You can pay from ｣100 to ｣2000....your choice

As is often repeated in scope discussions, look through as many as you can, when looking take your time, look near and far evaluate the picture you are seeing, imagine shooting bits within the sight picture with the reticle...and as I have said but will repeat do not chop and change, only change after you have really tried to learn what you have but its not working for you.