I have installed a complete irrigation system in my garden, but would like
to use grey water if possible. (Water would be from the bath, shower and
hand basin)

Am I allowed to use it in my own garden?

If so, do I need to do anything to the water to make it suitable for use?

The current system takes water from the roof and stores it in 2 1450 Litre
containers (above ground)
The filtration I have on this is a simple mesh bucket (Used for planting
plants in ponds) followed by a bucket of gravel (The exit holes at the
bottom of the bucket are covered with smaller pond plant pots, so the gravel
doesn't escape!)
This then drains into a small water butt, a pump then pumps the water into
one of the 1400 litre containers, this is then connected to a second one at
the bottom, and a high pressure pump then delivers the water to the
irrigation system.

I was thinking of installing a small tank with another pump (with a float
switch) that would also feed into the 1400L containers, but was unsure if
the water needed some kind of treatment to remove soap etc.?

Thanks for any advise, or pointers!

Sparks