The 'market' was decimated. Any providers that worked on smaller margins were wiped out (we were with People's Energy and they were one of the first to fall - now stuck on a terrible tariff with British Gas). Without any competition the remaining providers will coin it in. In time new competitors may appear but that's a long way off.
Arguably those failed companies weren't set up with sufficient resilience and we should be grateful for the likes of Centrica for keeping our utilities working. Alternatively the French model allowed the government to moderate the price spikes and it's no coincidence that French inflation is the lowest in the EU and much lower than ours (it is, of course, adding tens of billions to their national debt).
The problem most had was offering fixed-price supply for 12/24 months, but not hedging against price increaes. I guess their rationale was that energy prices had been stable for several years and without the costs of hedging, they could offer cheaper pricing. The more established suppliers did hedge, hence they're able to honour fixed-price deals for the full terms.
Additionally, in France, nuclear power generates ~70% of electrcity there, with gas under 8%, so they've not had the huge increases in feed-in costs.
The UK has around 36% of its electrcitiy from gas-powered stations. Only 17% from nuclear (~30% from wind/solar/hydro)
(Germany is 12% gas; 24% coal; 50% renewables)