The businessman said: “The best case would be to not take best deal off the table prematurely, which is membership of the single market, continuation in the customs union, which is what the Conservatives are doing.
“From that position, to get the other deals we need in terms of security, on the environment which keeps us safe and healthy.
“Unfortunately, they have taken that off and so if we get the Conservatives winning, we are likely to come out of that almost certainly.
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Roland Rudd warned Theresa May’s rhetoric might backfire during Brexit talks
“And then the best case is some sort of free trade agreement but I am concerned the Prime Minister (has) identified the European Union leaders as the enemy, and that they'll see her as the enemy.”
The business chief, however, added a hung Parliament could result in the UK remaining inside the single market and customs union.
Mr Rudd said: “Now hopefully a lot of that is rhetoric during a political campaign, but boy does it need to change immediately after the election.
I am concerned the Prime Minister (has) identified the EU leaders as the enemy
“And if it is a hung Parliament, then I think all bets are off and I think the likelihood is we probably would stay in the single market and the customs union.”
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Mr Rudd also claimed Theresa May’s “no deal is better than a bad deal” approach was "clearly wrong”.
Matthew Elliott, former CEO of the Vote Leave campaign and senior political adviser at Shore Capital, however, said he was confident in Mrs May’s ability to negotiate Brexit.
He said: “I'm even more a backer of Brexit now than I was (pre-referendum).
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Jeremy Corbyn during a visit to Hackney Marshes Football Pitches, to highlight Labour's manifesto commitment to ensure 5% of the Premier League's television rights income is diverted to the grassroots game, during a General Election campaign
“I’m confident that there will be a win-win situation.”
Mr Elliott said he expected Mrs May to remain in No 10 after the General Election while adding business confidence would plummet under a Jeremy Corbyn government.
He said: “I would be astounded if the prime minister wasn't re-elected.
“Business confidence would really go through the floor if Labour got in.”