Do I need to pay my first Direct Debit payment upfront?

It depends on the supplier. Some will take your first payment at least 10 days after your switch is completed. Others will take payment immediately – in which case you may end up paying your final bill with your old supplier and your first Direct Debit with your new supplier in the same month.

This isn't money you'll lose – it goes into your account as credit to pay for your future energy use, and if you build up lots of credit you can always ask for it back, or you'll be refunded when you switch again.