UK finance jargon - in plain English
An automatic payment authorised by you, controlled by the payee.
A direct debit is a payment instruction that lets a company pull money from your account on agreed dates. You give them permission once, and they handle the rest, including any changes to the amount. Direct debits are covered by the Direct Debit Guarantee, which means if an incorrect amount is taken, your bank must refund it immediately on request. They're commonly used for energy bills, broadband, council tax, and insurance.
You set up a direct debit for your energy bill. Some months it's £90, others £130 depending on usage or a provider update. You authorised it once and the amount adjusts automatically. That's convenient, but it means a provider could change the amount without you noticing, which is why it's worth glancing at your bank statement regularly.
Numbers simplified for illustration. Actual energy costs vary by tariff, usage, and provider.
Confusing direct debits with standing orders. With a direct debit, the company controls the amount and can change it. With a standing order, you set the amount and only you can alter it. Cancelling the wrong one can result in missed payments you didn't see coming, so check which type each payment is before cancelling anything.