how cold?

im from yorkshire england and its getting fucking freezing . well about 2/3/4 deg on a nite.
what i want to no is ?.
i have 5 girls on 12/12 in my garage in a closet under 400 hps in soil, in the day the temp is ok cos the lites and fans are on, but on a nite when i put em to bed 9pm till 9am. when i go look in a morning the plants are very cold. what i want i no is how cold can they take whilst in darkness b4 things start going wrong. ps its going to get colder. should i bring my set up indoor.
any sugg.

Best way is to always plan ahead.If you know it will be cold at the end then its best to have your lights on at the coldest hours such as night to add heat and off during the day so they stay cooler. Temps below 60-65 can be an issue with slowed growth and development.You can add heating lanket under pots to warm roots of a small space heater with fan to blow warm area in the grow areas

could i switch my 12 /12 from 9am on 9pm off the other way round, will it hurt my girls there 5week 12/12

Can you put any kind of heater in there that doesn't use light as the heat source?

I live in Lancashire and myn are outside! They have three weeks left of flower so yu should be ok mate. You can buy plant fleeces if your really worried that should keep them. It all depends on strain tho as to wether they can take extreme cold you should be ok tho mate

sk#1. bigbang.are the strain