I have been suffering with constipation but then a few times this week have leaked yellow watery stools without warning?

Severity determines: Occasional incontinence of stool with fecal leakage is common, but loss of bowel control particularly without warning may signal a significant infection, inflammatory problem, maldigestive concern, or neurologic disorder. Sometimes, particularly in youths, the condition is behavioral. Often, anal manometry followed by biofeedback can be curative without the need of surgery or medication.

Incontinence...: Fecal incontinence is usually the result of problems with the anal sphincter. There are several causes of anal sphincter dysfunction but in your case perhaps you have developed hemorrhoids (swollen veins in the anal canal) from constipation which can affect continence. I recommend addressing the constipation with stool softners and fiber. If problem continues then see your doctor.