Complex sentence: Macarthur had gained the right to return to Sydney through lobbying, but would not accept the conditions imposed that he admit his wrong doing and promise his good behaviour and so he remained in England until Lord Camden granted him unconditional return to NSW in 1817.
Split into simpler sentences: Macarthur had gained the right to return to Sydney through lobbying, but would not accept the conditions imposed, namely that he admit his wrong doing and promise his good behaviour. He therefore remained in England until Lord Camden granted him unconditional return to NSW in 1817.