It could well be down to bad estimates.
According to this White Paper: Statistics Used by the Query Optimizer in Microsoft SQL Server 2008, when you use local variables,
If you use a local variable in a query predicate instead of a parameter or literal, the optimizer resorts to a reduced-quality estimate, or a guess for selectivity of the predicate. Use parameters or literals in the query instead of local variables, and the optimizer typically can pick a better query plan.
I haven't found anything for 2012 which retracts that statement (and my minimal testing shows it to still be true)
A simple way to check this is to use sp_executesql to run the query, and pass in your variables as parameters.
Remove the table variable and use the TVF fn_GBCAA directly in the query.
IS that TVF multi-statement ? If so, see if you can rewrite it as an inline TVF.
MM
select geometry::STGeomFromWKB(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