BIRMINGHAM, England (Reuters) – British finance minister Kwasi Kwarteng said on Monday he would publish details “shortly” on how he planned to bring down public debt as a share of economic output over the medium term, addressing concerns among investors over the cost of his recently announced tax cuts. “Today we face new challenges and in addressing those challenges, we will act in a fiscally sustainable and responsible way,” Kwarteng said in a speech to the annual Conservative Party conference. “That is why, shortly, we will publish a medium-term fiscal plan, setting out our approach more ful…