A serial fundraiser famous for taking on huge physical challenges in a retro deep sea diving suit will hang up his metal helmet after on final monumental test of endurance.

Leukaemia survivor Lloyd Scott, who has raised over £5 million for charity since his diagnosis 30 years ago, is preparing to complete an "ultra marathon" underwater for Sport Relief.

The 56-year-old, from Theydon Bois, will travel with his team to Anavilhanas National Park in Brazil and the small town of Taucapecacu in January next year before he commences his marathon down the bed of the Rio Negro.

Mr Scot, who works as a sports centre manager at Leytonstone School, will spend seven days in his metal suit in his bid to reach Encontro das Aguas where the Negro meets the Amazon.

He will be forced to navigate through dense undergrowth in fast flowing currents, while avoiding some of the Amazon's most dangerous predators including caiman crocodiles and piranhas.

The former professional goalkeeper and fire-fighter was diagnosed with leukaemia in the late 1980s, days after he saved two children from a house fire and was receiving treatment for smoke inhalation.

He made a recovery from the illness after a bone marrow transplant in 1989 and has since devoted his life to raising cash for good causes.

Mr Scott has completed over 40 feats of endurance for charity, including cycling across Australia on a penny-farthing, an underwater marathon in Loch Ness and swimming from John O'Groats to Lands End.

In 2002 he set the record for the slowest ever marathon when he completed the London Marathon in his diving suit in 5 days, 8 hours, 29 minutes and 46 seconds.

He has walked to both the North and South Poles and raised funds for charities including Children with Cancer UK and The Queen Elizabeth Diamond Jubilee Trust.

Scott was awarded an MBE for his services to charity in 2005.