Brian Vale, a naval historian and author of A War Betwixt Englishmen, Brazil against Argentina on the River Plate. 1825-1830 has kindly allowed me to quote his comments on the Protest recorded by Captain Leith of the Concord

"The conversation [between Stewart Leith of the Concord and Jaime Costas of the Vencedor de Ituzaingo] here is convincing. International law permitted countries in a state of war to declare blockades. But to be legitimate, blockades have to satisfy a number of criteria.

One was that ships had to be aware of the fact of a blockade and sufficient time had to elapse between the declaration and its enforcement. For example, it was assumed that it would take 2 months for notification of a blockade of the Plate to reach Europe. Thus, if it was declared in (say) January, then no ship which sailed from Europe before April could be legitimate prize since it clearly did not know about it and could not therefore be a deliberate blockade-breaker and thus liable to arrest.

Another was that to be legitimate, the State which declared the blockade had to have enough ships to enforce it. The official British, American and French view was that Buenos Aires (with only half a dozen warships and a two dozen officially licensed privateers) could not possibly blockade the whole coastline of Brazil! This is the point the captain of Concord makes. It was also the reason that the vessel was taken back by HMS Ranger. If the blockade had (for example) been limited to the waters around Rio, then the blockade would have been officially legitimate, and the Ranger would have taken no action.

One can understand why the captain of Concord raised these points ["that at the time the vessel sailed from England no accounts of such Blockade had been received there nor did he suppose that the Buenos Ayrean Government had a sufficient force to blockade any one Port"], but in fact Costas was acting in accordance with his instructions and with normal practice. Whether a detained ship was a legitimate prize could only be decided by a legal Prize Court: it was not for Costas to make that judgement. Where Costas broke the rules was by removing the weapons from the brig. Cargo had to be sealed and left untouched just in case the prize was ruled illegitimate in the Courts and the ship and cargo were released. Of course, the pistols were obviously legitimate contraband of war and liable to seizure so he must have assumed he was running no risk.

Since the Concord was retaken by HMS Ranger, the case never reached an Argentine Prize Court. However in the settlement of claims submitted by the British Government after the war and settled in 1831-4, compensation of £1920 for damage to ship and cargo was awarded." Brian Vale, private communication,. September 2006.