The three above species are naturally found in Southern Europe close to the Mediterranean region, where summers are long, hot and mostly dry, and where temperatures can reach 100F+.
Tortoises are reptiles and require heat which they regulate by moving in and out of the sun during the day. Night temperatures are often much lower (around 60F - 70F). A tortoise can maintain a higher body temperature in the wild at night by digging into the soil which has been heated by the sun during the day.
Apart from the importance of the temperature, tortoises can be exposed to high levels of ultraviolet light (UVA and UVB) from sunrays which also plays an important role in the health of the tortoise. UVA and UVB help increase appetite, activity and induce reproductive behaviour. It also helps the tortoise produce its own D3 vitamin, which helps absorb and distribute the correct levels of calcium in its body which it needs to maintain healthy growth.
The difference between the weather in the UK and Southern Europe is massive. In the UK, we have on average 1000+ hours of sunshine per year, whereas in Southern Europe there are 2,500-3000+ hours per year. It is quite clear that there is a massive shortfall of sunshine producing both heat and UV (essential to the survival of tortoises) in the UK.
In their natural environment, winters are much shorter and summers much longer than ours. This means that tortoises can be awake and active from the beginning of March until late November, enjoying 9 months of good weather. In the UK, the two most problematic periods of the year are spring and autumn. This is due to unpredictable weather producing fluctuating temperatures; one day it could be warn and sunny and the next day could be raining, frost or even snow. In fact, our weather only starts to settle mid to late May, extending to mid September before night temperature start to drop pushing them back into hibernation. This would only give a tortoise approx 3.5 months of good weather which is considerably less than the 9-month period in their natural habitat. You can now understand that tortoises left outside all summer and hibernating for an unnatural long period of time tend to become ill or die within the first few years. This is why it is so important to have both outdoor and heated indoor enclosures to house them in periods of unstable weather and to increase their summer months.