I was thinking more of times where it's been very cold at Thorpe or Towers and rides have been up and down...It could be a UK H&S thing, they may be able to run at -5 technically, but legally they can't.
For example, 27th Oct 2018, every coaster apart from The Walking Dead was down for most of the day, not for lack of trying, they were popping online at times, but just went straight down again. So I can't imagine it was regulations that were the main issue, or they wouldn't have been able to get a couple going for one of the coldest hours in the evening. (Stealth ran that evening for at least an hour.) The temperature was about 3 or 4 degrees with no wind, rain or snow in the day. dropping to 1-2c in the evening.
I had pre purchased coaster fast tracks for the kids that day, so had reason to reach out to Thorpe about it, and this was their response... They do mention H&S, but for reasons I mention in my last paragraph, I don't but that, they also imply that their coasters just don't like the cold, which made more sense on this occasion.
Thank you for your email regarding your recent visit to THORPE PARK Resort!
Firstly, I would like to apologise that your day with us did not live up to your expectations. We want all guests to have a great day with us so it was disappointing to learn that this was not the case for you and your group.
Unfortunately on the 27th October, We experienced some delays with the operation of our rides due to adverse weather. This affected the operation of seven of our rides as they were unable to operate in low temperatures. These temperatures are set by the manufacturers of those rides in accordance with Health and Safety regulations. In anticipation of the forecasted cold weather we did increase the availability of other attractions. With Living Nightmare, Saw Alive and Vulcan Peak opening at 12pm and Blair Witch Opening from 3pm. We also extended the operating hours of The Walking Dead:The Ride until 11pm. However I can see that this may not have fully rectified the enjoyment of your visit.
Due to this we have activated our Island Return Guarantee which means you can revalidate your entry tickets for use on selected dates during our 2019 season by bringing your tickets or booking confirmation to our admissions team at the entrance of THORPE PARK Resort.
Either way it's good news.Merlin are yet to comment, which makes me doubt they will go for proper all year opening, but we'll see. The real message I'm taking from this is that the council are going to be more supportive of the park going forward, and we perhaps may see some limits removed and hopefully changes like longer opening hours or longer fireworks.
They do have the makings of a really good winter event, they just need to get a few more coasters open. If they could open Wickerman, Spinball, Oblivion and Smiler (I dunno, give the ride computers cozy winter jackets or something,) then along with the smaller rides, and Cbeebies, that'd make the park a very worthwhile winter visit.
They even have 5 or 6 all weather dark rides at their disposal when the new one is built. Curse, Hex, Sub Terra, Granny G, Dungeons and Horizon.
I think what I'm trying to say is that, recent investments position the park (either deliberately or coincidentally) in a better place for year round opening, they just need to get a handful of the coasters working in colder weather, and they could have a full theme park offering in the winter.