JUSTIN TALLIS/Stringer via Getty A Brexit "endgame" may force a last-minute trade agreement between the UK and European Union, a chief strategist said on Thursday."There is so much at stake for the UK" that failure to agree on a deal would deliver a major blow to the recovery in the economy, Jeffrey Kleintop, Charles Schwab's chief global investment strategist, told Business Insider.Prime Minister Boris Johnson will most likely strike a last minute deal in mid-to-late October, giving a significant boost to UK financials and the pound, he said.UK stocks have declined over 20% this year, sharply underperforming other European markets.Visit Business Insider's homepage for more stories.