I assumed when I bought LLs t15 that I would be able to easily match its specs to a ballast here...but did not fully appreciate the complexities of MH bulbs/e ballasts. Can anyone advise me of what I should be looking for and if poss a UK based place to get it.

WOuld hate to have to wait for another thing to be shipped across the world:(

Cheers

You can use any 400W electronic metal halide ballast.
I'm not sure if a direct link would be possible, as we are not allowed to link to competitive websites, but try this Google search: 400W electronic metal halide ballast +UK