I think the others have almost covered it, but basically you need to use non-locking snares, with the permission of the landowner, making sure that you set your snares in an area where you are as certain as you can be that you are not going to be in any danger of snaring cats, dogs, and/or livestock. Don't forget, a snare does not only catch things around the neck. A snare set in the wrong place can do horrendous damage to a sheeps foot before you return to check it. (Which should be once a day MINIMUM, preferably once every 12 hours)
There are traps which are legal to use in the UK. These have to be of an approved design (it used to be MAFF that overlorded this but I suppose it might be the EA these days?) and are only legal if set under cover. This means you need to use a trap like the Fenn Trap and set it only in a tunnel or a burrow. Traps set above ground are a hazard not only to livestock, pedestrians and pets, but are illegal as they can be set to capture protected species such as birds of prey.
It is also illegal to set snares to catch any species of deer in the UK.
As for methods of snaring, the best I can desribe without the aid of diagrams is this....
Set your snare in between the pads on the ground where the rabbit run shows the rabbits are putting their feet down as they hop. This will help to ensure that you snare your rabbit "mid hop", making for a more certain capture.
Tether the snare FIRMLY to a stake driven into the ground off to one side of the run (This is what the cord on the snare is for) This stake wants to be at least a foot long and an inch in diameter. In softer ground, make it bigger, you would be amazed at how strongly a snared rabbit can pull. The snare needs to set above ground level by being trapped in a split in the top of a small twig. Trap the wire BEHIND the main oval loop, next to the loop that joins to the cord in this twig and have the bottom of the main loop about as far from the ground as the width of your hand across the base of your fingers (3 1/2 to 4").
You can often improve your chances of getting a rabbit or two by setting your snares within 10 feet of a fencline where the warren is one side and the field they feed on is the other side. Set your snares on the field side of the fence in the more heavily used runs then go back to camp. Last thing before bed that night, walk across the middle of the field with a torch on and make a bit of noise. The rabbits that are out in the field will bolt for home, and are more likely to become ensnared in their hurry to get there than they would be whilst more cautiously coming out to feed. A quick check along the line of snares as you return to camp will often result in a rabbit or two. Snares can be reset for first thing the next day, or lifted now if you have enough meat for the pot already.
If you return to your snares and find that one or two of them have been successful, but all you are left with is the head of the rabbit, it simply means that your technique is fine, but that Charlie fox beat you to your dinner!
Good hunting!
