hi william, as kezo says for the lease just ending you will receive £600 plus the £250 one off new lease bonus.
now if you ordered your new car before 1st oct, that lease too will be worth £600 in effect, so you will get £350 shortly after getting the car and then at the end of the 3 years you will get the new gcp of £250.
if however you ordered your new car after 1st oct it will just be the new gcp £250 at the end of that lease.