For a BMI of 31 you would expect someone 6ft 3in to be 17.5 stone.
With a BMI of 31 if you were applying for life or disability insurance in the UK you are likely to receive non standard rates (possibly +25%) but this will depend on the insurer. Obviously if you are rated you are then required to disclose this fact in future.
Getting it down to and at keeping at 16 stone sounds good advice.