Methyl's link says:
"We'll also give you a 3 month interest-free overdraft
For the first 3 months of an agreed overdraft, we won't charge you interest if you use it.
Conditions apply – see footnote 2"
Footnote 2 says:
"To be eligible for the 3 month interest-free overdraft on our FlexAccount, all we ask is that you use our Account Transfer Service to switch your existing Direct Debits and standing orders when you open your new account. When you apply we’ll ask you for the details of the bank account you want to switch. Don’t worry, switching to us is easy, and we can manage it for you."