I guess they do not want E7 people.
N-Power Sign Online Dual Fuel V18 Electricity - Day...... 4.98p inc VAT (*1) Electricity - Night ...10.67p inc VAT (*1) Gas ....................... 2.42p inc VAT (*1)
(*1) Less =A350+=A350 annual discount on those prices or about 10-12%.
Gas is half the price - but has higher capital, maintenance, teeth sucking & maintenance cost.
If you are North facing, detached, poorly insulated, then it is a pretty much a no-brainer to use gas.
If you are South facing, semi-detached, well insulated (and I do not mean just windows!) then E7 can be viable but I hate the lack of true radiant heating so it is relegated to bulk-hall & bedroom heating. Living areas get proper radiant which is so much more comfortable than anything except underfloor which is the ideal (with heat-pump or GCH or I suppose E7 if you can get a row of tanks!).