Cold can cause nutrient deficiencies. Phosphorus is typical and you get purpling, but other physiological ills are not unusual either. You can get potassium deficiency symptoms too in overcast weather due to low light. It is not that easy to tell K vs N vs Mg deficiency so consider what ferts you used and also the conditions.
In a glasshouse situation, I find it better not to spray anything on the leaves ever, take advantage of the fact they are never rained on, which is a giant plus for tomato leaf health, generally. Once a week, pick off all the leaves that look nasty, because even if it's physiological a disease can get in there on the damaged leaves, so it's as well to remove them.
It's true I don't bother with sprays, some people do and in some situations it must be worthwhile or necessary, but I assume everyone has to remove diseased plant material from tomatoes, whether you are spraying or not. I just find that doing so is actually enough (and ferts help too of course!).
So whenever you prune and tie up, make sure you get the bad leaves off and the plant will of course produce more in a jiffy.