Complex sentence: But he was quickly prised away from de Gaulle by SOE, who used him as a liaison officer with the Bureau Central de Renseignement et d'Action (BCRA), the Free French intelligence agency.
Split into simpler sentences: But he was quickly prised away from de Gaulle by SOE. But the SOE soon used him as a liaison officer with the Bureau Central de Renseignement et d'Action (BCRA)-the Free French intelligence agency.