Not a heater, a heat lamp. In the wild, turtles bury themselves deep in the mud and hibernate during the winter months. Obviously, this isn't possible for a turtle who lives in a tank. It is dangerous and unhealthy to let a captive turtle go into hibernation.
A UV heat lamp will simulate the summer sun and provide the Ultra-Violet (UV) light that your turtle needs, so the turtle will stay warm and go through the winter without hibernating. You can buy a UV heat lamp to put/hang over the tank at most pet stores, including Petco. You can even buy a timer for the tank (not at Petco, though, for some reason), so you don't have to be home to turn it on every morning, and off every night.
I have included two links: one to the Petco page where you can buy Zoo Med Reptile Basking Spot Lamp bulbs, and a lamp to put those bulbs in. The other is to a website called X10.com, where you can buy a timer for the lamp.
No, red-eared sliders are not illegal in England.
Yes, red eared sliders do hibernate only in the winter and if you keep your turtle inside then it should not hibernate if you keep your turtles warm.
yes, mini red eared sliders do exist
Yes, red eared sliders eat minnows in the wild and in captivity.
Red-eared turtles can eat cilantro. If they are not eating lettuce, you should try feeding them it.
never
no
no
yes they can be separated because by nature, red eared sliders are solitary creatures.
no
humans
It is natural for red eared sliders to shed, it only means they're growing! Take care of em the same as you'd treat a RES that isn't shedding at the time (: