ATP to ATPL
It can take much less than a year - just get written exams out of the way - you can do revision courses with the likes of Bristol Ground School. Pass the ATPL exams, then go to CAA and give them your VISA card, licence and logbooks to get CPL issued or take MPA type rating and get ATPL issued. You can get the MCC for free because you ahve over 500h Multi Crew type experience.