The contract was created under Indian jurisdiction. I am currently employed under UK branch of the company which is a multi national company from India

Hi I have been transferred to UK from India in 2009 by my employer on Tier 2(ICT). The initial assignment was for 6 months and I have signed an agreement with my employer before coming to UK that I would have to work for 6 months in India before I resign. I am now on Indefinite leave to remain after getting multiple extension and I have got an offer from another employer in UK but when I resign from my current employer, my current employer is advising me that I have to work for him at India for 6 months before I resign. Please can someone advise if I have to follow this. I have negotiated with my employer on this but they advise that I can't avoid this. To separate from this job, I have to server this employer for 6 months in India. Please can anyone advise what should be done in this case. thanks.