I genuinely am confused by the email. It says
“
The Energy Price Guarantee caps the average unit rate to 34p / kWh (this number varies by region) — and with a smart time–of–use tariff, that means the combined average of your off-peak and peak rates is capped at 34p.
So although your day rate is above 34p, the Government’s rules are very clear: we can’t apply the subsidy because your night rate is so low, and overall you’re already paying less than the Energy Price Guarantee ratesfor your electricity.”
But ((20*40)+(4*7.5))/24 is 34.58. So above 34p. So either the email is numerically inaccurate or they actually mean the blended rate on the bill based on actual usage (which for most will be under 34p)