[ZeroGravitas]

Article on this phenomenon, sometimes called the "spark gap":

https://www.lowcarbonhub.org/p/spark-gap/

The UK is worst in Europe and has been as high as 4.7x recently, more than the average Heat Pump can overcome.

[darkr]

It would only need to be 4.7 to beat a gas/oil system that is 100% efficient.

In reality, a very good gas based system that is well specified and installed might reach 80% as a whole. Most UK gas/oil heating systems are significantly lower.