Is there a payment processor extension for Worldpay or do we need to create one?
It looks like there is experimental code available on Github for a Worldpay processor, which might need further development.

You may also want to explore the Omnipay extension. It doesn't list Worldpay on the extension page yet, but there is a driver for Worldpay with Omnipay that may just need some testing and/or minor tweaks to get running with CiviCRM using the Omnipay extension.