CDs aren't 'region-coded', so they'll work anywhere in the world.
DVDs, however, do have regional codes. A DVD purchased in the UK will be coded to Region 2. That means that it will play on any DVD player purchased in Europe. (For some strange reason, Region 2 also includes places as far apart as Japan, South Africa, Greenland and countries in the Middle East).
A standard DVD player purchased in Australia will play Region 4 DVDs. (As well as Australia, Region 4 includes New Zealand and, somewhat strangely, South and Central America).
However, most DVD players are actually manufactured 'region free'. The regional coding is only added at the very end of the manufacturing process. This can usually be removed by a simple 'hack'. (Typically, that might mean nothing more complicated than opening the disk drawer and entering a 3 or 4 digit code on the remote control). Licensing agreements mean that retailers shouldn't sell 'region free' DVD players but they're allowed to sell 'region coded' players together with the instructions on how to remove the regional coding. (Yes, I know it's daft!). So it's not hard to obtain a 'region free' DVD player.
In short:
Yes, UK CDs will play in Australia.
No, UK DVDs won't play in Australia unless they're played on a 'region free' player.
Chris