A new study argues that Theresa May's combative stances have united EU leaders...
The academics, working on the UK in a Changing Europe initiative, warned attitudes to the United Kingdom since the June referendum have hardened.
One of the reasons for this change in stance is believed to be the approach Theresa May has taken.
A key issue is expected to be the "divorce bill" which will be presented to the UK by the European Commission, which reports suggest could be as much as £50bn to £60bn.
The report's authors say that would be "a considerable embarrassment" politically for the UK's Prime Minister.
London School of Economics assistant professor Sara Hagemann said the prospect of Brexit has "united the EU27 to a degree rarely seen before."
"While several of these countries first expressed the hope that a solution would be found to keep London 'closely involved in EU affairs', attitudes are now quite different," she said.
"The UK Government is seen as working opportunistically with only UK interests in mind and little consideration for wider European issues and priorities."
The key moment in the Brexit negotiations is expected to be the EU's response to the triggering of Article 50.
Dr Angus Armstrong of the National Institute of Economic and Social Research wrote: "If the continental consensus is that the UK is still living on Fantasy Island, we could be heading for a showdown sooner than anyone expects."
The authors believe Mrs May is probably aiming to take Britain out of the single market and will seek a free trade deal for goods and sectoral agreements to allow as broad as possible access for services.
Immigration would be brought "fully" under UK Government control, resulting in a "large fall" in EU migration to the country.
The report, titled Brexit: Six Months On, warns that divisions within the Conservative Party and the Cabinet itself may "hamstring" the Prime Minister as she finalises her position in the weeks before the tabling of Article 50.
A DExEU spokesman said: "We're preparing for a smooth and orderly exit from the EU and by working together with our European neighbours we're confident we will be able to secure a deal that works in the mutual interests of both the UK and the rest of the EU."