It is possible at every bank to transfer money to a different account, as far as I know. Tap "Pay" in the bunq main screen, choose an amount and enter the IBAN of the account you want to transfer money to.

UK banks don't always use IBANs though, but if you change the currency to GBP in the bunq send payment screen (bunq's Transferwise integration will be activated to achieve this), you'll be able to choose either IBAN or UK Sort code + Account number for the recipient.