As David said, in the UK (or certainly the UK where this tent would stand up to local climate) you don't need a heat source so any you provide is a luxury/bonus. The candle lantern? not a lot of heat given the drafts you will get in these tents, a paraffin hurricane lantern will give a lot more and a gas lantern would see you toasty warm.
How many winter hill walkers take a dedicated tent heater with them? Not a lot, many moons ago when I was winter camping in Snowdonia or the Brecon Beacons we would cook on a Primus stove often in the tent or tent doorway ( I know
) and then just get snug in our sleeping bags.
The human body throws out a lot of heat and that heat when trapped in a sleeping bag suitable to your situation will see you sleep just fine.
The thought of woodburners in these little tents as suggested by some frightens me.
Sorry to drag this up, but a woodburner of any kind in a tent that small is an accident waiting to happen