Sir Ben Ainslie has said he is “astounded” after Sir Jim Ratcliffe’s Ineos Britannia team announced a parting of ways with the four-time Olympic champion for this year’s America’s Cup. He also threatened to launch a “significant” legal fight in response.

Ainslie’s crew overcame Italy in the Louis Vuitton Cup series to qualify for the showpiece event for the first time since 1964 last year. However, Emirates Team New Zealand went on to claim the Auld Mug in a 7-2 win in Barcelona last October.

Following the defeat, Ainslie – who won the America’s Cup as part of Team USA in 2013 – vowed to come back stronger with the next bid to end Great Britain’s then 173-year wait for success in the event.

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Yet on Thursday Ineos announced that, while there will be another challenge launched, Ainslie would not be at the helm, with Dave Endean appointed as chief executive of the team’s project.

“Ineos will enter a challenge for the 38th America’s Cup under the team name Ineos Britannia after parting ways with Sir Ben Ainslie,” a statement from Ineos read. “Unfortunately, Ineos Britannia and Sir Ben could not find agreement on terms to move forward following the conclusion of the 37th America’s Cup in Barcelona.

“Ineos Britannia has appointed Dave Endean as CEO, who brings immense experience in sailing and the America’s Cup. Ineos will also continue to leverage the design and technology expertise of the Mercedes F1 team under the guidance of technical director James Allison.”

In response, a statement from Ainslie’s team on Thursday read: “The British Challenger for the 38th America’s Cup, led by Sir Ben Ainslie, was astounded to read today’s statement from Ineos and Mercedes F1 regarding their planned challenge for the 38th America’s Cup. This plan raises significant legal and practical obstacles for them that will play out in the coming days and weeks.

“Furthermore, Sir Ben Ainslie’s British America’s Cup team will be known as Athena Racing going forwards, aligning with the British Women’s and Youth America’s Cup team, the Athena Pathway.”

The Ineos chairman and Manchester United co-owner Ratcliffe feels that despite the departure of Ainslie, the team has a strong base for the next challenge. “I am enormously proud of what we achieved in Barcelona in developing a British boat that was truly competitive for the first time in decades,” Ratcliffe said. “It set new benchmarks for British sailing, including winning the Louis Vuitton Cup for the first time, and taking races off the defender in the finals for the first time in 90 years. We will now build upon this for the 38th America’s Cup through the Ineos challenge and already have 100 scientists and engineers working on the design of our AC38 yacht.”