How much do you need to take off the pedestal - thickness of a tile or the thickness of timber sheet + tile? If it's only the tile you could try using a small angle grinder to grind it down otherwise you probably need to move the sink.
If you are using the grinder - be patient, grind in as slow a speed as you can, also try for slight bumps on the top or bottom that might help if removed.
Don't hit it with a hammer or you will end up with more than an inch off of it the best solution is to raise the sink an inch if the water pipes are copper you will have to extend them also.
As Ainya says why would you not cut the tiles to fit around the pedestal rather than go cutting/damaging anything else? Don't forget its a lot easier to adjust the floor tiles rather than replace the whole suite because the pedestal gets cracked.
tiler was a cowboy (claimed he'd do a great job - it ain't all that great as far as I can see - sorry i didn't give it a go myself!) - he just left without putting the pedestal back in - so i reckon he knew it wasn't going to fit and just ran!
I just need to loose the height of a tile - only a tiny bit off the top.
after paying for the tiling, i don't want to fork out more money to get someone to move the sink or the tile (or get the tiler back in), trying to figure out what i can do about it myself!
The only way to do this is to raise the sink. Anything else will be a botched job and you'll be looking at it for a long time. It's a job that even a mediocre handyman should be able to handle with relative ease.
Deffinitely raise the basin. As the tiles are already down, you won't get a neat finish if you try to remove around the pedestal, and you are very likely to break the pedestal if you try to modify it.
You could take the opportunity to fit isolating valves if they are not already fitted.
Leo