Thanks for all the replies guys, (I didn't get them till now as my e-mail has been broken).
The good news (for me, I guess) is that my barrel is a Youngs barrel with a pressure release valve on the lid.
Over the last couple of days, I've poured out a glass or two and it's extremely cloundy...
I've just done my first brew (a budget larger kit) using one of those heated mains powered glass sticks to aid fermentation at the right temp. It seems to have gone well and I checked that it was ready to barrel with a hydrometer.
Although I knew that I only needed about 3oz priming sugar in...