For shipping you will need to use the custom logic. If you can explain how you want the shipping calculated we can help you set that up.
For payments, credit cards and cheques can be done using the Offline gateway.
There is a PayPal Gateway available for AgoraCart, it is a members only file. So, if you are a paid member of AgoraCart, you can get the files, as well as all sorts of other hacks & more advance support.
The PayPal gateway does support GBP.
HTH!
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God Bless!
Bonnie - AgoraCart Moderator
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