Thanks for replies, just to get get a bit more of a handle on it. Thanks for the advice on the person access and tractor access gates; that sounds useful. Only roe here and on neighbouring ground.
If you are sure [member=28951]Steph Hen[/member] that you only need to consider Roe deer*, then a fence between 1.2m and (preferably) 1.4m should be OK. Mine is somewhere in between and I've had no Roe encroachments despite having a significant local population of Roe with very frequent sightings and well-worn deer track-ways on my acres !
My fencing comprises UK high-spec' rabbit mesh on the bottom and a 50mm chicken mesh above. The rabbit mesh has an out-turn at the bottom laid over the ground outwards (rather than being buried) and was pegged down on installation. (However, once grass has grown through the out-turn, pegging-down is not really needed.) I also have a high resident population of rabbits, but none have broached the fence or gateway after years.
Gateway: timber plank inserted into the ground under the line of the gate and rabbit mesh/lower timber plank added to gate. To deter Roe deer leaping the gate, some tall angle brackets have been added to top of gate with fishing line strung between. (Deer don't like dealing with stuff they can feel, but can't quite make-out by sight - apparently!)
*If your area has a population of Muntjac deer, then you might need to be rather more careful. Seemingly they can/will climb fences: if they are around in any significant number in your part of the UK you might wish to also consider an out turn at the top of the fence especially on a 1.2-1.4m rabbit/Roe deer fence.