Thanks Bigenuf and Philip

Your instructions will be a big help.

Philip you can't refresh the cancel page as it redirects you to another page.

Bigenuf. I've been able to use your instructions and make this work for me. Although, at the moment i've kept the head and side bars on as currently you only need to turn off whitelisting in RBS inorder to keep using the base tag until it is enforced at the end of this month. but at least I now know I can sort of fix this.

I also added my concerns to RBS worldpay and received a very quick response shown below.

Thank you for your email on 10.09.2009 about the recent changes in our system.

I am sorry that you experience issues using the payment service since we have implemented a series of changes on our platform to comply with the latest PCI DSS standards.

We are fully aware that this is effecting our customers who are using Zencart and we have highlighted that this is causing issues with the payment process.
Adding the <base href> tag onto our whitelist is currently being looked into.
Hopefully we are able to correct this issue as soon as possible. We have acknowledged your complaint and added it to list.