I presume that you mean that a UK company is providing a service to a Norwegian company with an "office" on Guernsey.
You can only issue the invoice to the Guernsey office if this is a Permanent Establishment for VAT purposes and this PE can be seen as the recipient of this service. EU case law was recently launched on this but that goes far beyond this forum to elaborate on.
From an UK perspective your service will likely qualify as B2B service and will be outside the scope of UK VAT (you have to check the specific UK regulations on this). Norway is non EU territory anyway. I am quite sure that a local Norwegian type of reverse charge will apply (applicable on intangible services), called SNUDD AVREGNING.
My guess is that UKco wouldn't have to charge UK or Norwegian VAT.