From what I understand you are looking for a post undergraduate certificate, not a MA, right? In that case University of London offers two programs which may be of interest: http://www.londonexternal.ac.uk/undergraduate/dip_grad/economics/index.shtml or http://www.londonexternal.ac.uk/postgraduate/soas/econ_princ/index.shtml
It is not exactly a certificate, but you can take up to 15 graduate credits in economics relatively inexpensively through Cameron's MBA program. You can always contact them about just taking the econ classes ECON 5023 Economic Concepts ECON 5113 Microeconomics ECON 5213 Macroeconomics ECON 5313 Managerial Economics ECON 5933 Issues in Global Economics http://www.cameron.edu/online/mba_degree_prog.html
thanks for the feedback. ant idea why one of the London programs is 900 pounts and the other is over 6000 pounds?
Because the cheaper program is at the undergraduate level. UofL has created an alternative route for undergraduate certificates and degrees for those already holding bachelors degrees. In the case of bachelors, I think you're expected to complete 8-9 papers rather than the normal 12. The other program is at the graduate level. It's for those who don't have an extensive background in economics.