Complex sentence: Eurosceptics believe that the UK would prosper outside the European political and economic bloc thus seek withdrawal from the European Union; the "portmanteau" "Brexit" is sometimes used as an abbreviation for a British exit from the EU.
Split into simpler sentences: Eurosceptics believe that the UK would prosper outside the European political and economic bloc and seek withdrawal from the European Union. The "portmanteau" "Brexit" is sometimes used as an abbreviation for a British exit from the EU.