I need a printed invoice for our accounts department

No problem! Head over to the My account page, and click on View & pay invoices button. From there you can click the "View / Print" link next to any invoice.

This printable invoice includes a link which can be used to pay the invoice without the need to be logged into wormly.com.

Note that you can also modify your Company Profile (linked to from the printable invoice) to include your address, VAT number and various other items so they appear on the invoice.