The government approved issuing of on the spot fines for not carrying poop bags when walking your dog. Within the Anti-Social Behaviour, Crime and Policing Act there is a section called Public Space Protection Order. This includes dog fouling. The fines are between £80- £100. If the fine is not paid in a week then there could be a penalty of £1000.
The law is used by an increasing number of councils that choose to enforce the stricter rules on dog fouling. A council may also dictate the number of poop bags to be in your possession to prevent a fine. There is risk of punishment for an honest citizen that normally carries bags and picks up after their dog has defecated. There is potential that the owner gets fined after using the very last poop bag and heading home, or does not have the specified amount of poop bags remaining when stopped. The discretion on issuing the £80-£100 fine depends on the character and opinion of the person issuing the fines.
It may be wise to keep 2 emergency poop bags separately from where you normally carry your poop bags. Consider folding two bags very small and putting them inside something you always carry e.g.; a phone case, wallet or bag.