Hi have been a legal sec before. ILE is probably your best bet. Legal secretary is not as hard as medical secretary to be honest, as I have done both.
Legal sec is better paid then med s it's not the NHS! but of course you don't get the pension benefits. If you find the right law firm then you can get great benefits such as private medical insurance, parking, gym membership etc.
I would contact ILEX, but to be honest unless you want to become a legal executive, then there is no point in doing a lega sec qualification as I have never met a legal secretary with one and I have been in the legal field for 7 years.
Jobs are fairly obtainable to be honest, as long as you can type 60 wpm, can audio type, take calls, arrange files etc then your already a legal sec.
Also it depends on what area of law that your a secretary, as there are so many different areas of law and you mainly specialise in one...i.e. employment, conveyancing, commercial litigation, family etc. Usually a secretary can do numerous areas of law, but secretaries are also expected to fill in forms to help the solicitor out, but again you will be shown how to do this and the forms vary from each area of law.
Hope this helps, if you have any more questions then feel free to ask and I'll try and do my best to answer them.