I wish to install an outside socket. Currently there is an exterior fuse box, and a buried cable that used to go to a barn that has been taken down, i want to connect to this supply. It is to run to a chicken paddock to power an electric fence some 30 meters away. I looked on screw fix but iam a little bewildered as to what I need seems there is more than one type of armoured cable of course. Any advice pls.
You don't really need low smoke and to run an electric fence I would guess on less than 1 amp supply and so likely the thinnest cable would do the job.
However you may in the future want to run more so at 30 meters with 13A to be within 5% volt drop the cable needs to have less than 29mv/A/m rating and 1.5mm² cable is just on limit so I would say 2.5mm² cable would be better selection.
There is also an earthing problem at 30 meters and although it may be OK without seeing the set-up I could not say as to any issues and it may need a TT but in some situations TN-C-S supply may be OK.
As agricultural and horticultural premises the supply must be protected by a RCD depending on how terminated this could be 30ma, 100ma, or 300ma. Likely 30ma at 40ms and again because agricultural and horticultural premises the fittings must be IPXXB or IP2X.
Again with agricultural and horticultural premises the depth of cable burying is also in regulations 0.6m or 1m min.
You will also need to refer to Refer to BS EN 60335-2-76 which I don't have a copy.
This is not a DIY job and to produce test certificates would be hard for any non electrician and I would strongly advise you get someone who is conversant with the requirements to do the work for you.
SECTION 705 of BS7671:2008 does give some of the requirements. But I know that some electric fence units especially from New Zealand can require a good supply when running miles of fence. I do remember fitting them in the Falklands and seem to remember needing to sink earth rods easy in their peat soil but in UK I would need to read up about safety before knowing what is permitted. I Falklands electric fences were least of our worries it was those with scull and crossbones signs were were more worried about!