Power circuits here (on the ring main system) generally use 2.5mm cable, with a 30-32A breaker at the main box.

Remind you that 32A on a 2.5mm2 is only acceptavble in a ring circuit, where the current goes through 2 2.5mm2 wires in parallel. For one conductor in most cases the absolute max safe current is ~13A for 1.5mm2 and ~20A for 2.5mm2

I have 1 electronic fluorescent in my shack its a 36 watt single tube but the thing is its plugged into a normal socket on the same circuit as all my other stuff including a 1.5 Kw heater and several power supplys now I do have varistors and capacitors across the mains to my radio gear which is powered by the above power supplys do you think I need to worry about my electronic lamp?  The whole shack is supplied via a 1.5 mil cable from the house around 60 feet away

With long runs of thin cable you might get a problem of breakers not tripping in time in case of short circuit, as the cable resistance alone limits the current below what the breaker's instantaneous trip point

In this case, the cable (both poles combined) is about 1/2 Ohm, so ~400A short circuit current, not yet an issue for C10 or even C16 breaker (though C16 is too high for this cable anyway)

The cable for my shack is protected by a 13 amp fuse in the plug at the house end and this is backed up by a 15 amp rcd

SOX meant 16 amp rcd

How is the cable fed to your shack, is it protected in some way from being damaged.?

And how large is the Variac ?

Curious question... What would be the effects of a capacitive load on a power system?

If the capacitive impedance becomes dominant, two problems will arise:
- It may cause the voltage on a long wiring end to become higher than at the source side. It is called "Ferranti effect" and in fact it is a result of the wire inductance to form a step up transformer. Those familiar with power RF knows this well, it happens with long wiring on a mains frequency too. The problem is, the usual distribution management sets the voltage at the distribution transformer to the allowed maximum, assuming the voltage will go down behind the line. Butonce the line is loaded with a capacitance and without much real power load, the voltage may go up, exceeding the upper bound without the management system knowing that.
- Other problems are running induction motors. The thing is, once you want to disconnect a leg, where you have induction motors, as well as too much capacitance, the disconnected system becomes a hugeselfexcited induction generator without any voltage regulation. That means a lot of the mechanical energy in the motors rotating mass turns into a strong overvoltage, limited just by motor core saturation. And that means more than double peak voltage, with huge energy behind. Way more severe overvoltage than the ferranti effect, even without any need for long wiring or so.
Mainly the second one is the reason, why all phase lag PF compensation is designed to remain a bit on the inductive side, never turn capacitive (here I mean just system parameter tolerances like capacitor capacitamce close to the maximum tolerance, not malfunctions like extinguished lamp,...).

The cable to my shack is clipped to a wall all the way from house to shack so its out of harms way there are some large bushes which hide it from veiw over most of its length. 2nd ive never heard of Ferrantie effect could this be partly responsible for the notable dip in voltage when the heater switches off the dip is only momentary lasting only a fraction of a second it doesn't happen every time and sometimes the lights simply go brighter as you would expect

Oh forgot to mention my variac is rated at 2.5 amps or 575 VA