i am also in the UK, i would never ever ever ever, move my plants into my garden for sunlight, IMO it doesnt compare to my 600watt HPS light, my plants have their nice cosy grow room to relax in all day and night, i wouldnt put them outside for shit, especially in the UK, us UK guys no that the weather changes its mind at all times, so having it outside for 2 days when the weather is good, then putting it back inside for the next week whilst the weather is shit will just confuse your plants. Just think, when your in your grow room, do you find it a bit of a challenge to see due to how bright your HPS is? because i do. but when you walk outside in the UK on an average day, do you find it a challenge to see due to brightness? because i dont. just my opinion though i guess. Happy growing anywayss. GW