Limits for human embryo research have been changed: this calls for public debate

A significant problem, however, is that there is no longer any limit on the time frame for research. Would it be permissible to do research on human embryos that are 20 days old or 40 days old? The guidelines specify no limit. The longer a human embryo is allowed to grow, the more recognisably human it becomes. At what point would we regard the research unethical, and at what point does the moral cost outweigh the benefits of research?