Questions about moving into a new school as an immigrant 17 year old

Hi! It had been one of my biggest concerns recently, considering the fact I'll be moving into the UK in three weeks that if I'll be able to continue schooling with the same grade as I am in now.

I will be moving from Sri Lanka, where 17 is where you start ALs, whereas in UK you start ALs at 16.I have already completed 5 months of my AL course in the Edexcel Curriculum here. Will I have to move in with the 16 year olds in year 12 or will I be able to move in with the year 13s. If it is year 12 that I have to join, will there be other 17 year olds as either other immigrants or kids repeating the school year?