You may not need any qualifications to become a neighbourhood warden, although some employers may prefer you to have a good general standard of education with GCSEs in English and maths, and experience of working with the public.
Employers will often focus on your personal qualities and people skills. It may be an advantage to have a clear understanding of the issues faced by the community you will be working in.
You'll usually have induction training, lasting around 12 weeks, while you get to know your area and the issues you might face.