Only smart meter data is currently accepted by the National Grid ESO Winter DFS scheme.
Additionally, since we will be giving notice of the event in advance for National Grid DFS powerDOWN events, energy savings will be calculated based on your forecast and what you are likely to consume, rather than what you were actually using just before the event.
This also helps to protect us and the grid from the system being gamed (turning on something right before the event to earn points is not helping the grid much!)
TIP: You can check if your electricity smart meter is working in smart mode by using the Citizens Advice smart meter checker - https://smartmetercheck.citizensadvice.org.uk/