"top-slicing"?

What is the meaning and the origin of "top-slicing"?
It was used in reference to the creation of Serious Organised Crime Agency: "Britain, along with Belgium and Germany, has about the most decentralised system in the EU and so this represents a top-slicing of the policing function"

The dictionary (infoplease.com) explains "top slicing" as "mining of thick orebodies in a series of stopes from top to bottom, the roof being caved with its timbers as each stope is exhausted".
But it doesn't make the metaphorical usage clearer for me.

Top slicing is also a financial/accounting term. It is commonly used in the UK; I don't know about elsewhere.

It refers to the removal of part of a budget so that it can be used to fund some centralised service.

I used to work in a University IT department. Some universities give each faculty an IT budget and they use that to fund their own local service. Some, like the one I worked in, 'top-slice', i.e. they take the percentage spent on IT from the total university budget and use it to fund a centralised service.