I did mine 6 months ago or so, through a course run by North Kent College. 3 days total, 2 theory and 1 practical out on a workboat, followed by an exam on the 4th day. It was pretty tough as the level of detail they need is high, and the relevance they give to ribs was fairly low!! Need to know amongst other things:bridges, reaches, wharves, buoys, reporting points, barrier procedures and the local port regs. Have a peek at the PLA website and get revising the docs!! Oh yeh, I didn't get it, but someone I know managed to get some sort of grant to help with costs...?
Good luck, pm me if you need more info...