I have a range of indoor plants and unfortunately with them, I have
little
flies.... What can I do to the soil, plant or other to prevent them from
spawning?!

They are probably hatching from within the compost in your potting mix.
Could you seal over the top of the pot up to the stem of each plant
with panty hose? When flies hatch they might be unable to escape and
the colony should soon die out. That's my theory, anyway.

Thanks John, like your answer ;o) Although I'm not willing to try it!

Someone mentioned putting soapy water in the soil.... Has anyone heard of
this working?