Well here’s how it's actually done. They don't make each stick of rock separately, they use a lot of mixture and make one giant sausage shaped stick of rock, then its pulled and rolled until it is very long and thin, then cut to the sizes which you buy them at.
The middle white part of a stick of rock is made by heating sugar, glucose and water to a temperature of 138°C (280°F). Once this exact temperature has been reached, the mixture is poured onto a water cooled table then most of it gets transferred to a pulling machine. The pulling machine has three metal arms which constantly rotate crossing over each other which give the mixture plenty of air which turns it white. The rest of the mixture that doesn’t get transferred to the pulling machine gets coloured and is used for the letters.
The coloured mixture is then put on a heated table. The letters have to be made big enough to stretch the length of the rock (about 1.2 metres long and 30 centimetres in diameter). The letters are made by taking long flat red strips of mixture and wrapping around the white mixture to form the letter, a bit like 3D lettering.
For example, to produce the letter 'O', a piece of white mixture is rolled by hand into a thin solid roll. A piece of the red mixture is rolled to form a flat strip and gets wrapped all of the way around the white roll. Then if you look at it from the end, it'll look like an 'O'.
This is then wrapped by the rest of the white mixture and then wrapped by a coloured casing.