it seems odd to me that Investec are offering different deposit rates on different currencies ... is it connected with prevailing dep rates in Australia ?
This is totally normal. Deposit rates are primarily linked to base rates in that currency zone. The ECB base rate is 1%, the Australian base rate is much higher.
Ciaran,
Looking at the Investec.ie website, I see that they mention "In July 2002 Investec became the first South African group to list in London and Johannesburg by implementing a Dual Listed Company's Structure"
Which of the companies is the one that operates in Ireland?
Secondly, If you go to the credit ratings on the same website, what interpretation should I take from this regarding risk on an AUD deposit account for 12 or 24 months?
Investec in Ireland has the same parent as Investec in London, which is Investec in South Africa.
If your deposit is under 100,000 EUR equivalent, then you are fully protected by the FSA/UK government.