Tier 1

Dear Eveyone

I have been reading some of the posts here re.Tier I visa  and found the info here very useful.
I am a dentist who has spent 4 yrs in Uk in permit free training visa upto 2004. I have also a full GDC registration. Since I still maintain my registration in UK i wondered whether i could do locum jobs in the hospitals in uk. I understand that I will need a tier I visa for this without a job offer being available. My question is how many years is the validity of this visa and what will happen when this period is over.. My intention is only to work in UK for 1 or 2 months a year as locum. Iwill still be keeping my job in India and only taking a few months break every year. If such is the case will I be able to apply for extension once this period of Visa is over and also will I be able to qualify for indefinite leave to remain after that.
Thank you