President-elect Donald Trump's plans for fiscal stimulus are "budget-busting" and markets should be more skeptical, a leading international economist has told CNBC Tuesday. Adam Posen, president of the Peterson Institute for International Economics and a former member of the Bank of England, said that although he is a pro-stimulus fiscal dove, he is unsupportive of the Republican's plans which strike him as "generally kind of ridiculous." According to Posen, "The size of the fiscal stimulus…is very large, unfunded and open-ended. Most of the things he wants to do in terms of tax cuts are likely to be low-multiplier rather than high-multiplier and budget-busting rather than responsible." Although the highly regarded economist does not have a problem with the idea of encouraging public-private partnerships, he pointed out that the private sector has deliberately chosen not to invest in recent years when it had the opportunity to do so. In his words the focus on pushing such joint investments is"not a substitute for a responsible fiscal policy and it's not going to move the needle in a big way."

TPP to be abandoned?

A soaring beacon of hope: The Freedom Tower at One World Trade Center. Spencer Platt | Getty Images

Turning to global trade, an area widely expected to be severely hit under a Trump presidency, Posen lamented the abandonment of the Trans-Pacific Partnership (TPP) by the U.S., saying it was a high-standard deal that would have implemented standards and protect property rights, amid other benefits. The TPP is a trade agreement among 12 Pacific Rim countries, notably excluding China, which U.S. Congress said they would not pursue following Trump's election last week, despite years of hard-fought work on the deal by outgoing President Barack Obama in recent years. The economist warned there would be a huge trade and strategic diversion to China once the U.S. stepped away from the scene. According to Posen: "It's going to be China setting the rules, it's going to be China bullying its local neighbors potentially." "So these Asian countries if they say 'Well, I'm going to go with Regional Comprehensive Economic Partnership (RCEP)', China's trade agreement instead, it's actually a very fundamental shift," he cautioned. The end effect would be further disruption to reasons for wanting to invest in the U.S., he concluded.

‘No opposition in the UK’

Moving onto the EU-U.S. Transatlantic Trade and Investment Partnership (TTIP), Posen highlighted that most of the disputes between the sides related to issues such as intellectual property and technology rather than standards. Given Trump's vocal displeasure with how he believes the domestic tech sector treated him during the campaign, Posen posited that the president-elect may be more willing to entertain Europe's proposals in this sphere than the current administration has been. As for the other political earthquake of 2016, Posen said despite the U.K. government's efforts to make the population believe its negotiating strategy over Brexit matters, it actually doesn't. According to Posen: "It's totally irrelevant. It essentially comes down to one thing which is do U.K. companies still get access to the single market in Europe which for geographic, historic, institutional and fundamental economic reasons will remain the most important market for the U.K. whatever else happens?" And the U.K.'s break from the EU is going to be sharp, in his view. "We're on path for a 'hard Brexit' - there's no political opposition int he U.K. that's going to stand up against it." he said.