The basics of the law is that cyclists must keep left (except under specific conditions) and not ride abreast (as in this photo), and cars must be darn careful and maintain a 1 meter gap at all times (as in this photo), and may cross the solid white line to abide by this law (as long as it's safe to do so).

Below is a summary of the responsibilities I mentioned:

The Regulations Require a Driver of a Motor Vehicle to:

1. Exercise due care while passing the cyclist.
2. Leave a distance between the motor vehicle and the cyclist of at least one meter.
3. Maintain that distance from the cyclist until safely clear of the cyclist. However, motorists may cross a solid barrier line to pass a cyclist provided that it can be done without obstructing or endangering other persons or vehicles. If it is safe to do so, it can and is done for a period no longer than is necessary to pass the cyclist.

The Regulations Require a Cyclist to:

1. Make the appropriate use of pedal cycle lanes where these are available.
2. Give conspicuous driving signals as contemplated in National Regulations.
3. Keep as close as possible to the left edge of the roadway.
4. Obey road traffic signs and rules.
5. Fit and use effective front and rear lights when riding in hours of darkness and when visibility is limited.
6. Not ride on the right-hand side of a motor-vehicle proceeding in the same direction, except when passing that motor vehicle or turning right at the intersection.
7. Not ride abreast of another cyclist proceeding in the same direction, except when passing that cyclist.
8. Not ride while wearing a headset, headphones or any listening device other than a hearing aid or while carrying another person on the pedal cycle, unless the pedal cycle is specifically equipped to carry more than one person.

Source: Safety of Cyclists and Blue Lights Regulations Announced

Finally, then, to clear up some confusion (that I certainly had) - the law requires a minimum 1 meter gap be maintained when passing a cyclist, but the Pedal Power association promote keeping a 1.5 meter gap. The 1.5 meter gap is probably just to play it safe, in case motorists underestimate how far 1 meter actually is (and because trucks 'n trailers sometimes have pointy bits that stick out wider than the driver may realise).

So, I reckon we try to keep that 1.5 meter gap whenever possible - and let's be a little more careful with people's lives. Ok? :)