It will truly depend on how soon you want to get into this field and what experience you possess. Whatever the qualification (either MSW or Diploma in Law) is, your experience in the field of interest counts as a pivotal point. Having seen the industry for more than 5 years, the field you want to get into is already filled with many professionals. If you really want to pursue further, you need to have a cutting edge over others. I think it's easier said than done; your ascribed competency (degree you possess) won't help you much in this regard. There is no dearth of people who have done the said courses; however, they ended up being nowhere. Hence, my suggestion would be "it does not matter what you do; but how you do it does matter."
Go with MSW, get into a good firm, get hands-on experience, then venture out to realize your aspiration of becoming a consultant in the field.
Regards,
Mahesh