Matt Sharp and Emma Pallent will be aiming to retain their titles when they compete in the Leukaemia and Lymphoma Research Blenheim Palace Triathlon on Sunday.

The event, which in it’s 11th year, is the second largest triathlon in the country and kicks off the season.

Sharp, from Enfield, who won the Under 23 World Championship in 2011, stormed to victory in last year’s elite men’s race, winning by nearly half-a-minute from Yorkshire’s Mark Buckingham.

The pair will be renewing their rivalry in the elite men’s race which starts at 9.25am on Sunday.

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Welshman Lestyn Harrett is likely to be a contender for the crown.

Of the Oxfordshire competitors, Daniel Crowe goes in the male junior elite, while Rosie Weston competes in the female junior elite race.

Ben Dijkstra and Edward Beecher tackle the male youth super sprint. Dijkstra won his age group at the London Mini-Marathon this year.

Half an hour earlier, Aldershot’s Pallent will begin the defence of her elite women’s title, which she won in great style last year, having been runner-up in 2013.

She will face a strong challenge from Alice Sharp and Sophie Coldwell.

In all, 7,000 competitors will be swimming, cycling and running over the weekend in one of England’s most spectacular private estates, which boasts a stunning freshwater lake.

Many are running for charity, including the Team Scarlett’s Dragons from Oxford’s Dragon School.

For the second year they have rallied together to support tenyear-old Scarlett Clarkson, who is receiving treatment for leukaemia.

Before competing they will meet up with Nicola Blackwood, the Oxford West and Abingdon MP.

Holby City actor John Michie will lead co-stars Don Gilet and David Ames in a relay team race for the sponsoring charity at around 1pm on Sunday.

Blenheim Palace will also play host to teams from three Formula 1 teams – Mercedes, Red Bull and Force India – who will be competing in a special relay race on Sunday, starting at 10.55am.

Each marque will have three relay teams representing them.

These include Oxford’s Matthew Storry, a senior systems engineer, Ed Cooper, 38, an aero model technician from Banbury, and Kidlington’s Andy Hallas, 36, a senior mechanical engineer, all of whom work for Mercedes AMG Petronas.

Cooper competes in the run and Hallas the swim.

“My individual aim for the weekend is to have a competitive swim and to be the first Mercedes swimmer out of the water,” said Storry, 35.

“I’d love to beat all the other F1 teams and have a Mercedes 1-2-3.”

Force India’s head of research and development, Andrew Brown, 39, who hails from Oxford, will compete in the swim leg.

Saturday’s action starts at 9.20am, with the last wave going off at 3.20pm.

On Sunday, racing starts 8.28am, the last competitors setting off at 3.10pm.