BERLIN, March 13 (Xinhua) -- The decision by Britain to leave the European Union has already sparked a collapse in international trade and capital flows, a study published on Tuesday by the Confederation of German Industry (BDI) warned.

The study cited recent data which showed that foreign direct investment (FDI) into Britain declined by a dramatic annual 90 percent in 2017 while Britain also fell by two ranks to fifth in the list of Germany's most important trading partners during the same period.

The BDI interpreted the development as an "alarming sign" that Brexit was already "casting a shadow" on economic relations between Britain and EU.

BDI director Joachim Lang urged London to seize the opportunity of an upcoming session by the European Council to present realistic proposals for a close future relationship between the bloc and the departing member.

"Our companies need reliability," Lang told the press here as he presented a list of the BDI's key priorities for a post-Brexit deal with Britain. "Preserve the status quo," was the first item on the list.

It called on London to at least agree to the continuation of current relations throughout a transition phase from March 2019 onwards to limit the economic fallout of Brexit.

Britain currently expects gross domestic product (GDP) of 1.4 percent in 2018, the lowest rate in the EU.

Due to the sluggish process of exit negotiations, German companies increasingly expect a "hard" Brexit in which Britain leaves the single market and loses most of its currently privileged access to the EU internal market.

"Tariff and quota-free trade in goods is the minimum requirement for German companies, ideally within the framework of a customs union," Lang emphasized.

Any less comprehensive free-trade agreement in lieu of customs union membership would carry the risk of logistical bottlenecks and inevitably lead to an increase in the cost and bureaucratic burden associated with trade, he added.