Mains supply to workshop

[Bushbaby]

I have a single fused spur running from the house to my garden workshop which powers everything inside (via the fuse box on an rcd):
- 2 fluorescent lights 
- a fan
- 2 very small dehumidifiers
- a 1.5 kw oil filed heater (on a timer in the winter and only comes on at dusk til dawn)
- 4ft heater tube (120watt - on all the time the winter/when very cold)
plus soldering and test gear when I working.
I'm aware that the oil filled heater will be the biggest source of drain. 
I really don't like this being on a spur (and inside, a spur on a spur). I'm really not sure that I can make an improvements but concerned that I could be putting too much load on the spur. Any thoughts??

Best Regards

Rob