It’s unlikely that your supplier will go out of business. If it does, Ofgem's safety net will make sure you’ll always have an energy supply, and will feel as little change as possible.
This guide will answer some of your questions.https://www.ofgem.gov.uk/consumers/household-gas-and-electricity-guide/extra-help-energy-services/ofgem-safety-net-if-your-energy-supplier-goes-out-business
On Line Tax Return
You can use the online service to:
fill in and send your tax return to HM Revenue and Customs (HMRC)
go back to a tax return you’ve already started
check your details, view returns and print your tax calculation
You’ll need to register for Self Assessment again if you’ve sent a tax return in the past but you did not have to send one last year.