One of the biggest hurdles is numeracy and literacy. To enrol in many courses now (e.g. NVQs) the applicant has to pass a basic literacy and numeracy test (which IS supported by the training provider) but this is a massive drawback to many people - who don't have basic skills, or who have basic but are not confident - since they have developed devious and skilled coping mechanisms over the years to disguise the fact that reading and number are difficult for them. You need to construct a very good persuasion about the benefits of enrolling in any course for these people - otherwise they will fall at the first hurdle, being reluctant to sign up in case their learning gaps are discovered. The big point for me is that my learners undertake these tests and are given support without it being made apparent to their employers - there is then no "shame" in finding reading and writing difficult, and they can go forward and complete the qualifications, with trainer support.
I find that it's not the desire for the qualification which is the drawback - it's the fear of not being able to do it, or to start and fail. That needs to be overcome very sensitively if this initiative is to succeed.