Complex sentence: There he had a clandestine meeting with Menachem Begin; the head of the Irgun underground organisation, he was wanted by the British armed forces and had a £500 bounty on his head.
Split into simpler sentences: There he had a clandestine meeting with Menachem Begin, the head of the Irgun underground organisation. Begin was wanted by the British and had a £500 bounty on his head.