It depends on your budget and expectations. Hairdressing is by no means a soft option.
If you can afford it and want to be working within 6 months, then consider an intensive high quality course such as the Sassoon Academy 24 week Diploma for £14.5K.
To be a competent hairdresser able to cut hair and do basic colour services, if you attend a local FE College, you’re looking at completing a minimum of NVQ/VRQ level 2 (ideally level 3 too) and a further couple of years of being supervised after that.
A high proportion of hairdressing students who complete the basic level 2, do not continue with a hairdressing career. I think many of them are not prepared for the number of hours of practice after qualifying, that it takes to reach a basic level of skill required. There’s a very good reason that Apprenticeships used to take around 4 years to complete.