[0] suggests (without a useful link and my searching has not found one) that Heathrow is doing 460GWh annually. Presumably[1] that equates to 1.25GWh daily (which could be where the 1-2MWh/day came from - a simple unit error)?

[0] https://www.bloomberg.com/opinion/articles/2025-03-21/heathr...

[1] I know precisely nothing about power consumption of large systems but dividing the annual figure by 365 seems plausible.