If you're an Australian under 30 (assuming some other general eligibility) you would fall under the "Youth Mobility Scheme" which allows you to apply for a working visa for up to 2 years. This is a fairly straight forward arrangement as UK/AUS are both Commonwealth countries.
I would just apply directly. As I mentioned, this is a standard visa for Aussies and going through an agency will just increase the costs for what is a pretty simple application process.
Information on the scheme and how to apply can be found here: https://www.gov.uk/tier-5-youth-mobility
Hope that helps!
Pearse 9 months ago