Currenty I put just 3-5mm of watter at the bottom of a saucepan, put a
lid on, turn the gas down very low so that the flame just comes on,
and use this to steam steam vegetables, fish, meat together, which
works a treat because the water at the bottom collects the juices
which I can then use to flavour at the end. So I use everything and
the method is extremely economical since I barely use gas and not
waste energy heating water to heat vegetables and then throwing it
down the sink again.

Using a steamer will be more flexible, but at the very least I want it
to:

1. Have a knob that controls the amount of power used to heat the
water since there is a minimum amount required that will boil the
water and there is no need to go over this.

2. Must be able to take a small amount of water, say 1/16 cup full.

I have found that although gas is cheaper than electric on a purely
cost/energy basis, the advantage of gas over electric is lost if gas
is ignited in the air to heat things since some of the energy is lost
to the surroundings, whereas an electric element heating water gives
all of its energy to the water rather than the surrounding air. On the
other hand, a steamer for a gas/electric hob satisfies 1. and 2. above
but will an electric steamer? Looking through the Argos catalogue the
electric steamers don't seem to satisfy any of the requirements 1, 2
above and so a hob steamer is my only option.

Thanks for your advice.