I was thinking more about GCSEs and exam centres as I understand this seems to be a stumbling block for many.
It can be difficult and the advice is to find an exam centre that will take independent candidates (you have to phone and ask - just cause an exam board website says they do it, doesn't mean they do).
Also I was wondering how easy it is to move from informal learning to a structured course and what are the key skills that need to be developed before this?
None, in general. My DS did an OU maths course two years ago which ensured he had enough of a grasp of maths to be able to do the A level from a standing start. My philosophy would be that you learn the skills you need when you have a reason to use them. I still support him, so I have downloaded past papers - having done one earlier in the week, he knows that today's mock paper in college was easier than if he had not done it, so he has now learned an important skill that he'll put into practice over the next few weeks (he takes the AS papers in January, having started in September).
I'd expect the same with English, or any other subject. It is OK not to have "study skills" (writing essays, research, taking notes etc.) as long as you are in a position to learn them (e.g. from a supportive teacher, parent or other mentor) when you need them. I teach a level 1 module for the OU and we provide a lot of support to students to tell them how we want them to present assignments etc. We do not penalise them at the start but as they move through the module, if they keep making the same mistakes, they lose marks.
Although it is early days for DD she may be interested in an art foundation course and I presume this would be more portfolio based but I wondered whether like many uni courses, maths and English at GCSE would be required as a minimum - can OU credits be used instead of these as well?
Unfortunately, the OU route is effectively closed off to most HE young people - from October 2012, OU study is funded from the same Student Loans pot as other degrees and using OU before going to uni will eat into the total amount they can borrow. There are often schemes that allow access at a cheaper rate (e.g. the current Access to Success scheme gives an access module and a full level 1 module for £75 to the student) but the standard rate is £1250 for 30 credits. Universities may accept 30 credits as being equivalent to one A level. My DC got in under the previous funding regime where part-time study was entirely separate and was based on the student's income, so they did most courses for free (and 30 credits were only about £450).
It now costs £2500 to study but AA100 is the humanities (60-credit) introductory module and is very good to prove ability to write academically. It covers art history, poetry, history, philosophy, culture, religion etc.