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They're probably the least well known member of the emergency services, but the North West Police Underwater Search and Marine Unit provide vital support to forces across the region.

From major investigations to more routine safety work, they help take a look at what's hidden beneath our rivers and canals.

Paul Salt went out to join them on an operation in the Leeds Liverpool Canal in Bootle, and met Sergeant Tony Darbyshire who is on secondment from Greater Manchester Police.