The idea behind the Tax Return was a form that could match the Tax Authorities required information so I would start with the taxReturn-detail metaSQL as the mechanism to retrieve your information. The Tax History is more detailed and transactional.
There are a lot of options available to you as to what can be done with the data. You can make use of the xt.parsemetasql() function to build a query exactly like the metaSQL provides. This could be accessed via an external source, or as I mentioned it would not be difficult to send that information via a REST API call to the Tax Authority.
As I mentioned in my other response, xTuple version 5 adds in Avalara Tax Integration. This external service calculates tax in place of the internal xTuple tax sub-system. While this service is intended to ensure compliance with the ridiculously complex spaghetti that is the US tax system, it does also include support for non-US tax systems including VAT compliance. In this case you can submit VAT Returns directly from the Avalara system.
So (as always with xTuple) plenty of options available.