They are the new OFGEM rules, the new suppliers has to pay the old supplier when you switch under certain circustances. They are calling it a 'market stabilisation' charge'.
The OFGEM representative was explaining the 'market stabilisation' charge' a while back on BBC Radio 4.
https://www.ofgem.gov.uk/publications/market-stabilisation-charge-dashboard
Maybe, easier to understand on Martin Lewis' site here:
https://www.moneysavingexpert.com/n...e-energy-price-cap-every-three/#stabilisation
"What is the 'market stabilisation charge' – and what does it mean for bills?
The 'market stabilisation charge' is a charge on suppliers when they sign up new customers. When you switch, the new supplier will have to pay this fee to the old provider if wholesale energy prices fall significantly.
It was introduced in April to enable suppliers that have bought lots of energy in advance – to cover the higher number of customers on standard variable tariffs right now – to recover some of the costs if wholesale prices drop suddenly and they see huge numbers of customers switching away from their standard tariff, according to Ofgem.
When it was introduced, suppliers would have to pay if wholesale prices dropped by 30% on the level Ofgem uses to calculate the price cap. The changes announced today mean that suppliers will now have to pay a charge if wholesale prices drop by just 10%.
Initially, the gaining supplier will have to pay the losing supplier 75% of the cost of the energy beyond this trigger point – this has now been increased to 85% following today's announcement.
This is worked out as a pound per kilowatt hour (£/kWh) charge which Ofgem will publish weekly. The charge is multiplied by the customer's annual usage and the gaining supplier pays that amount.
This could potentially kill the return of cheap deals for switchers if wholesale prices were to fall dramatically, as suppliers would have to bake these additional costs into the price of their tariffs."