"Cold and difficult" — It sounds more like the description of life on another planet rather than life outside of the European Union (EU) but that's how one former U.S. diplomat has predicted that the U.K. will find the world once it's left the 28-member bloc.

"The U.K., should it leave on March 29th, will find that the world is a pretty cold and difficult place without the leverage of the EU," Anthony Gardner, a former U.S. Ambassador to the EU appointed by former President Barack Obama, told CNBC Monday.

With just under three weeks until the U.K. is due to leave the EU, both the U.K., Europe and rest of the world are none the wiser as to what the country's future relationship with the continent will look like ahead of a series of votes this week that will determine the course of Brexit.

On Tuesday, U.K. lawmakers will vote on whether to approve or reject (as expected) U.K. Prime Minister Theresa May's Brexit deal with the EU. If they reject it, on Wednesday they will then vote on whether to leave the bloc on March 29 with "no deal." If they also reject that scenario (as expected) they will then vote on Thursday on whether to seek a delay to the departure in the hope of securing better withdrawal terms.

The latter is scenario seen as the most likely currently although whether the EU will make any further concessions or amendments to the deal on offer, when it has so far refused to do, remains to be seen.

If the U.K. leaves the EU with a deal there will be a 21-month transition period in which it hopes to negotiate a trade deal with the EU and to replicate up to 40 existing trade deals that the bloc currently has with trading partners around the world. The U.K. can prepare, but not implement, trade deals during the transition period.

So far, it has only signed a handful of "continuity trade agreements" to preserve current trading arrangements during the post-Brexit transition period, however, including one with the U.S., but these are not free trade deals (which it cannot sign as an EU member now and during the transition period).