Complex sentence: In February 2016, the UK government led by David Cameron negotiated "a new settlement for Britain in the EU" which was then followed by a referendum on the UK's membership of the European Union was then held in the United Kingdom and Gibraltar.
Split into simpler sentences: In February 2016, the UK government led by David Cameron negotiated "a new settlement for Britain in the EU". A referendum on the UK's membership of the European Union was then held in the United Kingdom and Gibraltar.