Preferably a Tokyo Marui but they are obviously expensive. £150-£200
TM VSR-10 Desert Version is £165 from Fire-Support.
http://www.fire-support.co.uk/product/marui-vsr-10-pro-sniper-rifle-desert-tan
The Marui rifles should have excellent accuracy and range due to their awesome (magic) hopups.
There is also a clone of the VSR called the BAR-10 made by JG which is good, but both the VSR and BAR are hard to find in the UK and abroad now. Out of stock pretty much everywhere unfortunately.
EDIT: Just as I write that I check on TaiwanGun and they're actually stocking BAR-10 rifles again! WANT!
http://www.taiwangun.com/en/3-in-1-sniper-set-bar-10-jg?from=listing&campaign-id=19
Alternatively I would recommend the Well Warrior L96. Like every other sniper (maybe except a TM) it will need upgrading to be much good (otherwise you may as well be using an AEG)
http://www.taiwangun.com/en/3-in-1-sniper-set-mb-01-olive-well?from=listing&campaign-id=19
http://gunfire.pl/product-eng-1152200729-Warrior-I-sniper-rifle-replica-olive.html
These are Polish websites, so you do have to ask them to clearly display your UKARA on the box. You can also write your number in the business line when ordering so it should show up.
It would be good to support UK retailers more but as aforementioned these can be hard to find in the UK AFAIK, and it could be a lot more expensive.
For upgrades I'd recommend Airsoft Sniper Parts UK (ASPUK)
http://www.airsoftsniperparts.com/
