Given that lavender likes it drier rather than wet, I can't imagine it would do well long term in a hydroponic setup. Can you plant them in a well-draining container mix instead?

FataMorgana

well not really because right now its absolutely freezing and hardly any sun so they'd die pretty quick

Actually, chirdi358, lavender is perfectly hardy in the UK. If you could transplant it into a pot and place it somewhere cool and light (conservatory? porch?) to harden off it could then be safely planted out in the garden. If you are in the far North or at altitude maybe you'd be best off waiting until the spring but I agree with Fatamorgana that Lavender is not a good candidate for hydroponics or indoor growing. The plant in your photo appears to have a fungal problem and warm damp conditions will just encourage it.

Here is a link that might be useful: Lavender being grown commercially in Scotland

I dont have any garden spance, it's all stoned and patio'd you see. Would lavender be able to grow in an unheated conservatory?

Yes, it would. But it would be even happier in a big pot on the patio.