Hi Steve,
What sharpening media do you have? Do you have a wetstone, maybe something like the India stone you can get at a hardware store? Do you happen to have a grinder? If not, get them. Doesn't need to be expensive.
First look at how the chisel looks like. If the edge is badly chipped, or the angle is way to steep, you might want to start on a grinder first. Clean the grindstone first. You can get a diamond dresser around 7.50 quid nowadys. Have a look at the adminster site or so. Then grind the bevel, close to 30 degrees. When the edge is chipped, I first remove the chipping with the chisel at 90 degrees to the stone. That makes a very blunt chisel of course! Then grind at 30 degrees. Press the chisel lightly against the rotating stone and move the chisel left to right to left continously. Feel with your fingers just behind the edge for heat (don't be afraid, the grinder won't bite you). When it gets warm to the touch, dunk the chisel in a nearby bowl of water. Continue until you have almost a sharp edge, just a little line of glistering still to be seen on the edge.
If you can feel a burr on the flat side of the chisel now, remove it. Lay the flat side of the chisel flat on the wetstone and move it back and forth until the burr is removed.
Then go to the wetstone, if it has two sides, start on the coarse side. Poor some oil on the stone. Put the bevel on the stone, and feel how it kind of clicks on the stone. Very easy to feel this. Have a finger near the bevel end to put pressure there. The other hand is also kind of low on the chisel to hold it on place. Now rub the chisel back and forth, using all the stone surface until you feel a burr on the flat side of the chisel. This is very important. As long as there is no burr, you haven't got a sharp edge yet.
Repeat on the fine side of the wetstone. Then remove the burr. Put the chisel with the flat face flat on the fine side of the wetstone, finger pressure just behind the and move it back and forth again.
You can now strop the chisel. With a piece of leather, or MDF, or even grocery paper. It should be flat, so glue it down if neccessary. Repeat the above sequence like how you did on the wetstone. This polishes the edge.
This procedure won't give you un "ultimate" edge, but more then sharp enough for the job at hand. It takes some practice, but you learn while doing. If you want to read a much better description of the process, follow this link:
http://www.antiquetools.com/sharp/