A Brazilian fisherman has landed a wall-sized slab of space junk emblazoned with the union jack while fishing in a remote Amazonian river.

The fisherman, named in local reports as Manoel Alves dos Santos, 73, found the debris, which is believed to be from the launch of Europe's most sophisticated satellite, in the river Uriandeua.

Ownership is in no doubt as the carbon-fibre panel is emblazoned with a British flag and marked "UK Space Agency" next to the logo of Arianespace, the European satellite company.

Locals from Salinópolis, in northern Pará state, were initially uncertain what the object was and – after 10 of them hauled it ashore – reported the find to a local military base.

The UK Space Agency said the object was part of the payload covering from a communications satellite, which was launched from the Kourou base in neighbouring French Guiana last July.

"The object found in #Brazil was fairing from the Ariane 5 rocket that launched AlphaSat #lostandfound," the agency tweeted. "It probably landed in the Atlantic and then floated inland," Julia Short, a spokeswoman for the UK Space Agency, told the BBC.

Inmarsat, the manufacturer, said Alphasat is the largest and most sophisticated European telecommunications satellite.

For the fishermen, however, the giant chunk of rocket was more likely to be seen as unwelcome rubbish. According to local media, the authorities have asked the UK to remove it.

• This article was amended on Thursday 1 May 2014 to correct the description of the object