And when you say resistive, do you mean element within (an electric) boiler, radiators to work as normal, or something more direct, electric radiators/underfloor/etc.?

I think it doesn't really matter much what is meant throughout - point was about shifting gas demand on to the electricity supply, and whether the grid could cope with it if everyone did that to a meaningful degree.

Resistive heating means using 1kw of electricity to get 1kw of heat.

Heat pumps use 1kw of electricity to get >1kw heat.

Not necessarily, it's just uncorrelated since it's not what's doing the actual heating.

Similarly a gas boiler uses 1kW electricity (for the pump) to get potentially >1kW heat out of radiators (and pipes). Because that heat is energy conserved from the gas, not the electricity.

Anyway I didn't mention heat pumps or compare them to resistive heating so I'm not sure what I'm defending.