A 457 Visa is a 4 year temporary visa which unfortunately the Australian government in years 2007 to 2013 has made a political football.
If you transfer your pension funds whilst on a temporary visa, and for whatever reason decide to leave Australia before you apply for and are granted permanent residency status, then you will have a huge tax problem to overcome.
Basically, if you depart Australia whilst a temporary resident your Superannuation fund into which you have transferred your UK pension funds is required to remit those funds to the Australian Tax office post your departure.
That payment to the ATO is then reported to HMRC back in the UK, who will then issue you personally with a tax assessment to the tune of 55% of the value of your Superannuation funds.
The advice therefore has to be, under no circumstances should you transfer your UK pension funds until such time as you have firstly decided to remain permanently in Australia, and then have applied for and been granted permanent residency.
Once that condition has been satisfied then by all means look at transferring your UK pension funds but definitely not before.