Complex sentence: When news of Thatcher's death became known, spontaneous street parties were held across the UK: celebrations took place in Glasgow, Brixton, Liverpool, Bristol, Leeds, Belfast, Cardiff and elsewhere, despite opposition from some of the local authorities.
Split into simpler sentences: When news of Thatcher's death became known, spontaneous street parties were held across the UK in celebration. These took place in Glasgow, Brixton, Liverpool, Bristol, Leeds, Belfast, Cardiff and elsewhere, despite opposition from some of the local authorities.