Are you looking for online courses in software security / secure software development, or more general courses in IT security (secure network engineering, pen testing etc)?
SANS institute http://www.sans.org has excellent online On Demand courses in all aspects of cyber security from management and auditing to pen testing, secure software development, secure network engineering, secure IT operations, Windows and Linux/Unix specific courses, incident management etc. The courses are comprehensive although expensive, and you can write certification exams which are well recognized in the US, not sure about the UK.
For software security I would recommend the Advanced Software Security program at Stanford University http://scpd.stanford.edu/computerSecurity/. The Foundations course provides a good overview of the issues in software security, and again you can seek certification. Stanford offers some free webinars as part of this program as well.
Security Innovation offers a series of courses on IT security and secure software development with an emphasis on Microsoft technologies and the Microsoft SDL: http://www.securityinnovation.com/products/elearning/index.shtml. The courses are short, relatively inexpensive.
All of these courses can be done part time, and should be available in the UK.