Hello Jools, you're right about your tomatoes, peppers and aubergines. They want a longer growing season and a bit of temperature to do well, so if you can keep them indoors til the weather warms up a bit it will save you some money on heating.
I think your flowers will be fine just kept above 5 or 6 degrees which is a growing temperature, and it's warmer than that during the day anyway, and at night you can cover them with fleece and set your heater to come on at 5 degrees.
When the weather's damp don't forget to ventilate your greenhouse to avoid botritus (gray mouldy stuff) . If your heater can be set to fan only it's a good idea to have it on for a while to help with the ventilation.
I think what we all need is an early spring. It's certanly bidding for it here and we haven't had winter yet.

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From each according to his ability, to each according to his needs.