Complex sentence: The Federation of Poles in Great Britain (ZPWB) which was set up to promote the interests of Poles in Great Britain acts as an umbrella for more than 70 organisations throughout the UK.
Split into simpler sentences: The Federation of Poles in Great Britain (ZPWB) was established to promote the interests of the Poles in Great Britain. Currently, the federation acts as an umbrella for more than 70 Polish organisations in the UK.