Unfortunately, X-Cart 5 does not have integration of "payment gateway hosted" type of Worldpay for UK so the only option available is using "merchant hosted" type of integration available via PA-DSS certified X-Payments only due to PCI compliance requirements.
If you need "gateway hosted" type of Worldpay - I suggest two options:
1) have it custom developed for your X-Cart 5 cart.
2) post an idea about such integration at
https://ideas.x-cart.com and let the community to vote for it. As soon as this idea gets enough votes X-Cart 5 team will pick it up and implement the integration. I am not sure how much time it might take though.