The eruption killed 19 people on the Caribbean island and British Overseas Territory in 1995, and forced thousands to flee.
A church service is being held at Shiloh Pentecostal Church in Dalston, east London, and is to be broadcasted live on radio across the Carribbean and live-streamed from the church's website.
The church has put on five coaches from Manchester, Leeds, Leicester, Birmingham and Eastbourne in order to bring Montserratians and others to the service, completely free of charge.
The theme of the service is the faithfulness of God, with Lamentations 3 the central reading.
It's hoping hundreds or even thousands of the 8000 Montserratians who originally came to the UK after the eruption in 1995 will attend, making the event a family reunion and celebration as well as one of remembrance.
Rev Roger Wade, pastor of Shiloh Pentecostal Church, was in Montserrat when the eruption happened.
He told Premier before the service: "Suddenly we heard jet engines roaring, and it was sounding like the Concorde... and so the government sent the defence force to investigate and when they got to the mountains found that it was a volcano that was lying dormant for over 400 years, that had come back to life.
"I would say [it was] pandemonium among the people... because here we were, most unexpectedly having our lives completely changed. And suddenly we found ourselves with a natural phenomena which most Caribbean islands and other places in the world have never experienced.
"We're expecting everyone [at the service], all 8000 Montserratians that came to the UK, we expect the majority of them to be there. We don't know where we're going to seat them, but we'll fill the streets of Hackney."
Listen to Premier's Aaron James speaking to Rev Roger Wade here:
