As nealglover says, they'll most likely have been nailed into wedges hammered into the brick course. This is not such a bad thing as it makes removing them a tad easier than if they're screwed in. If you're laying a new floor, any minor damage to the walls from removing the skirting may well be covered if the new skirting goes on top of the new floor.
If you do go ahead and try and remove them then:
Run a very sharp edge along the top of the skirting to break the seal between the caulk and the wall.
Then run a chisel along the line made by the sharp edge - helps if it's a cooking chisel rather than a shagging chisel.
Use a pry bar and small wrecking bar to ease the skirting off. Slowly slowly catch a monkey is key here. Use the pry-bar, then wrecking bar to ease out the skirting bit by bit. Put downward pressure rather than upward on the wrecking bar as you go. If at any point, you notice the plaster wanting to come away with the skirting, stop and cut it using the sharp edge or chisel. If there are any pieces behind a radiator pipe, then using a 10mm-ish drill bit, drill a line of holes (vertically), inside the envelope of the pipes very close to one another which you can then smash through with the chisel to "break" the skirting. How you then remove this piece is up to you.
There are lots o original features things worth saving in a victorian house when it comes to refurb, etc. Skirtings aren't one of them IMO as you can easily find exactly the same thing with which to replace them and decorate to a better standard than you can achieve trying to tart up old ones.