I planted one last spring in a sheltered position it did very well until winter which it did not survive. I dont think they are hardy enough for GB? You could try bringing it in doors till the frosts have stopped.

It should be outside, and a south facing balcony is perfect. It may be that it had been inside too long and needed hardening off before being left out all night, but more likely, I suspect you've not managed to keep it watered sufficiently well, and that's why the buds are dried out. Check the rootball to see of its potbound - if it is, you need a bigger pot and some ericaceous compost, or a mix of ericaceous and multi purpose, repot, and keep well watered. Standing in a pot on a southfacing balcony is a very dry, warm/hot place to be - I know, I've got one myself (a balcony, not leptospermum, lol). It will need to be given a bit of protection during winter, but should survive most winters perfectly well out there, other than if we keep getting winters like the last one.

Thanks so much for the tips! I have been watering it well but it may indeed be that it needs to be repotted. Fingers crossed that does the trick! (very heartened to have responses so quickly, I've never used this kind of site before!)