Having had a quick scan on internet, seems that most races have now banned them. whilst I cannot cite the exact ruling, ask yourself this: Is it worth the risk of disqualification to chance it?
As most races have distance markers, often every mile or km, would it not be easier and cheaper to wear a large display stop watch rather than risk upsetting the marshalls, and potentially having your equipment stolen!
do not expect a pb for this distance as there are a number of climbs en route but it is a good village event.
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