Thanks again Dean,
If you manage to locate the correspondence between SSS and Dom João I would be grateful.
In relation to the account of SSS and his contribution, contemporary and near contemporary accounts are always useful, but - as I’m sure you’re aware - do need to be treated with caution at times.

With respect, for British policy, see:

Frederick H. Black Jr., ‘Diplomatic Struggles: British Support in Spain and Portugal, 1800 – 1810’, (Unpublished PhD Thesis : Florida State University, 2005)
P. J. Cain and A.G. Hopkins, ‘The Political Economy of British Expansion Overseas, 1750–1914’, The Economic History Review, Second Series, vol. 33, no.4, 1980, 463–490
Christopher D. Hall, British strategy in the Napoleonic War, 1803-15, (Manchester : Manchester University Press, 1992)
~, Wellington’s Navy: Sea Power and the Peninsular War 1807-1814, (London : Chatham Publishing, 2004)
Wendy Hinde, George Canning, (London : Purnell, 1973)

Wendy Hinde, Castlereagh (Collins, 1981) – in my view still the best biography despite Bew’s recent work
Harold Livermore, ‘Portugal on the eve of the Peninsular War’, in Paddy Griffith (ed.), A History of the Peninsular War volume IX: modern studies of the war in Spain and Portugal, 1808-1814, (London : Greenhill Books, 1999)

John Lynch, ‘British Policy and South America’, Journal of Latin American Studies, vol. 1, no. 1, 1969, 1-30
Rory J. Muir and Charles J. Esdaile, ‘Strategic Planning in a Time of Small Government: the Wars against Revolutionary and Napoleonic France, 1793-1815’ Rory J. Muir, Britain and the defeat of Napoleon, 1807-1815, (New Haven and London : Yale University Press, 1996)
~, ‘Britain and the Peninsular War’, in Paddy Griffith (ed.), A History of the Peninsular War volume IX: modern studies of the war in Spain and Portugal, 1808-1814, (London : Greenhill Books, 1999)
Malyn Newitt and Martin Robson (eds.), Lord Beresford and British Intervention in Portugal, 1807- 1820, (Lisboa : Imprensa das Ciências Sociais, 2004)
Martin Robson, ‘The Royal Navy in Lisbon, 1807-1808’, in Malyn Newitt and Martin Robson (eds.), Lord Beresford and British Intervention in Portugal, 1807-1820, (Lisboa : Imprensa das Ciências Sociais, 2004)
~, Britain, Portugal and South America in the Napoleonic Wars: alliances and diplomacy in economic maritime conflict, (London – New York : IB Tauris, 2011)
Gabriel Paquette, ‘The dissolution of the Spanish Atlantic monarchy’, The Historical Journal, vol. 52, no. 1 (2009), 175–212

John H. Parry, Trade and Dominion: the European overseas empires in the eighteenth century, (London : Weidenfeld and Nicolson, 1971)

John K. Severn, ‘The Wellesleys and Iberian Diplomacy, 1808-12’, in Norman Gash (ed.), Wellington: studies in the military and political career of the first Duke of Wellington, (Manchester University Press, 1990)

And for Portuguese policy in general, the importance of Brazil and “Brazil Plan” in particular, see:
Valentim Alexandre, Os sentidos do Império: questão nacional e questão colonial na crise do Antigo Regime português, Volume 5 of Colecção Biblioteca das ciências do homem: História, (Porto : Edições Afrontamento, 1993)
José Luís Cardoso, ‘Free trade, political economy and the birth of a new economic nation: Brazil, 1808-1810’, Revista de História Económica, Journal of Iberian and Latin American Economic History, Año XXVII, Otoño 2009, no. 2, 183-204
Eurico de Ataíde Malafaia, ‘António de Araújo de Azevedo - Conde da Barca: personalidade exemplar de coragem e dignidade’, in Estudos em homenagem ao Professor Doutor José Amadeu Coelho Dias, vol. 1, (2006), 279-294
Kenneth R. Maxwell, Conflicts and conspiracies: Brazil and Portugal 1750-1808, (Cambridge : Cambridge University Press, 1975)
~, ‘The Atlantic in the eighteenth century: a southern perspective on the need to return to the ‘big picture’’, Transactions of the Royal Historical Society, Sixth Series, vol. 3, 1993, 209-236
Jorge Miguel Viana Pedreira, ‘From growth to collapse: Portugal, Brazil and the breakdown of the old colonial system (1760-1830), Hispanic American Historical Review, vol. 80, no. 4, 2000, 839-864

A.J.R. Russell-Wood, A world on the move: the Portuguese in Africa, Asia and America, 1415-1808, (Manchester : Cancarnet - Calouste Gulbenkian Foundation, 1992) Kirsten Schultz, ‘Royal authority, empire and the critique of colonialism: political discourse in Rio de Janeiro (1808-1821)’, Luzo-Brazilian Review, vol. 37, no. 2, Special Issue: State, Society and Political Culture in Nineteenth-Century Brazil, (Winter 2000), 7-31
~, Tropical Versailles: empire, monarchy, and the Portuguese royal court in Rio de Janeiro, 1808-1821, (New York and London : Routledge, 2001)
~, ‘The crisis of empire and the problem of slavery: Portugal and Brazil, c. 1700- c. 1820’, Common Knowledge, vol. 11, no. 2, 2005, 264-282

Stuart B. Schwartz, ‘Magistracy and society in colonial Brazil’, Hispanic American Historical Review, vol. 50 no. 4, 1970, 715-30

Best wishes
A