What is the origin of the phrase 'Down the banks'?

[allen ives]

She gave him 'down the banks' - Liverpool slang for giving someone a good hiding, metaphorically or actually. But why 'down the banks'? Where are the banks?

[dogfrank]

The phrase seems to be related to the numerous sandbanks within Liverpool Bay (The Mersey River). Going back to pirating days (exactly when, is unclear), pirates would lay in wait for the traffic laden with valuable cargo, particularly precious metals from the Americas, and would force them aground on the banks and nick the cargo. This appeared in a publication endorsed by the Mersey Docks & Harbour Board, and it's the only explanation in town, so.....