Complex sentence: Barkingside is chiefly known for the children's charity Barnardo's, the charity that was founded here 1866; it is in Barkingside where the charity's national headquarters are based.
Split into simpler sentences: Barkingside is chiefly known for the children's charity Barnardo's, the charity that was founded here in 1866. It is in Barkingside where the charity's national headquarters are based.