Well done on getting the job.
It pays to be honest in interviews as skeletons have a habit of very noisily dropping out of cupboards later on, this could lead to job offers being withdrawn or your new employment being terminated.
That said, unless you stood out as a poor employee, it's unlikely that your previous employer would mention it on a reference.
They do have the legal right to put any instances of gross misconduct on a reference, but only if they're giving the reference within the valid period of that warning, i.e. most warnings last for 12 months, exceptionally 24, after this they must be removed from your records.
In any case, if you had an otherwise good employment record, I really don't think you have anything to worry about.
By hte ayw, polish up yer grammer and puncuation!
