Hi Mavid,
A visit visa will be very hard to get - unless you can show you have significant ties to the Philippines to guarantee your return (successful, longstanding business/job, etc). Family ties are often not enough.
If I understand filipino family law correctly, a legal separation won't actually end your marriage in the Philippines - you'll remain legally married, but the legal separation allows the, well, "legal separation" of your assets, etc - but does not enable you to remarry.
In which case, you could have a problem getting a fiancee visa, if you are unable to marry legally in the UK (by virtue of your marriage in the Philippines). I could be wrong of course - I don't know if the Embassy will interpret a legal separation as being the same as a divorce/annullment..? Anyone else know any more about that?
However, what I don't know is if the Embassy will issue a finacee visa on the basis of your assertion that you will seek a divorce in the UK - indeed, I don't even know if that would legally end your marriage in the Philippines (as far as UK law is concerned, which is what would govern your subsequent eligibility to marry).
It could be that getting a legal separation is all that you need to do to get a fiancee visa (as well as, obviously, the normal onerous requirements on maintenance, accommodation, evidence of relationship, etc, which they somehow expect you to be able to magically stuff into an A4 envelope). If so, as Keith said, best of luck and I'm sure many members on here would be glad to offer titbits of advice, etc.
I for one would be interested to know whether a legal separation is enough for a fiancee visa. If it's not, your only option, as far as I can see (and I humbly wait to stand corrected if I'm wrong), is to obtain an anullment - a horrid, harsh, costly and time-wasting process in the Philippines, where the biggest cost will no doubt be the corrupt bribe - sorry, "fee", you pay the judge to get the anullment you want (and hope your husband doesn't oppose it with a bigger "fee".
I wish you the very best of luck in whatever you do - keep us all posted.
Take care