Much of the searches I did for "free tutoring online" bought up some pretty dodgy looking sites (hardly any of them actually free) teaching me how to become a driving teacher or learn Chinese, or other unrelated skills. Those that seemed to offer a wider area of expertise gave me a couple of chapters for 'free' then asked me to buy ridiculously over prices eBooks to learn the rest of the information.
Thankfully I stuck with it and after much painful searching I managed to find the below sites offering free tutoring online that were scam free:
Lesson Plans Page: The best site on this list for kids and adults (by some margin) which offers over 4,000 lesson plans for free. These cover a multitude of topics and are written by real teachers. You choose a topic, pick the age range and are greated with lesson plans. The topics I tried had up to 100 different plans, separated by sub topics and it felt like a good resource to get tutored for free.
BBC Bitesize: Harking back to my school days I remembered the BBC Bitesize website which offers GCSE help broken down by topics. You can take tests for each topic and watch videos online (which is a lot better than the days of staying up till 4am to record a video). Reading the expert guides is almost as good as sitting with a real tutor and as it's the BBC you won't have to pay a penny to do it.
Channel 4 Learning: Just like the Beeb, Channel 4 are also offering free learning resources. They cover a much greater range of ages from 5-19 with specific stuff per topic. The free online maths tutor is especially good and you can't fault some of the resources. There's even a separate mini site with 800 hours of free video tuition here.
Department for Education: The hardest site to navigate around and also the most formal, this is the official site for the UK Department of Education. Their best feature is the A-Z glossary as linked from the text on the left, which is a nice way of finding out exactly what is required for each level of education. Much easier to learn when you know what qualifications are required.
Free Lessons: The only search I could find which seemed to produce generally good results was typing 'free lessons' in to Google. This helped me find the excellent Home and Learn who offer free computer tutoring and there's many other sites on the list. Be sure to watch out for anyone trying to collect details or force you in to buying eBooks without telling you what's inside and you'll be set.