FCU off a single socket spur?

Hi all. I've just installed a burglar alarm in the understairs cupboard. The manual calls for a 2A FCU to supply the power.

Next to the panel, there's a single socket which appears to be a spur from another socket on the ring main as only one surface mounted cable goes into it. The single socket has a NEST thermostat plugged in permanently so not a high load.

I've read that a spur from a spur is a no no, but am struggling to see an issue with the load that a 2A burglar alarm and a NEST thermostat might produce.

Am I able to put an unswitched FCU next to the socket like this http://www.diy.com/departments/crab...ction-unit/241745_BQ.prd?icamp=recs&rrec=true, taking power from that, and put a 2A fuse into it for the alarm system, or if not, what's the best way of approaching? Replace the socket with an FCU handling both NEST and alarm?

Thanks for any help. Last piece of the jigsaw!

 

PLAN A:

Put the FCU next to the socket, as you suggested, but supplying the socket, not supplied from it.

Also have the FCU supply a socket or an outlet plate for the alarm.​

PLAN B:

Change the socket to a twin & plug the alarm in.​

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