If you refer to the following HMRC guidance:
Specifically…
Box 6 Total value of sales and all other outputs excluding any VAT. Some examples are:
supplies which are outside the scope of UK VAT as described in Notice 741A Place of supply of services.
Here is a definition of a Place of Supply Service. Any other non-UK non-EC items therefore should not be included anywhere on your VAT return.
where the place of supply of services is in a Member State of the European Community (EC), that supply is subject to the VAT rules of that Member State and not those of any other country. If the Member State is not the UK, such supplies are said to be ‘outside the scope’ of UK VAT
where the place of supply of services is outside the EC, that supply is made outside the EC and is therefore not liable to VAT in any Member State (although local taxes may apply). Such supplies are said to be ‘outside the scope’ of both UK and EC VAT
Regarding the sales nominal code…
I don’t think it would be wise to default any sales for non-UK customers to “General Export Sales”. Exports tend to relate to physical goods and not services so I’m sure many users wouldn’t want this as a default behaviour. I may be wrong so I will leave it open for further discussion.