If the wallet.dat was encrypted with a passphrase is there any relation to this passphrase and the private key allowing recovery? Is there any where else that this file or a copy may reside?
the harddrive on the computer is now full from re-downloading the whole chain and creating a new wallet.dat file making data recovery near impossible. Have used the public key to scan the chain and this definitely appears to be a new wallet as there are no transactions.
CE
There's hardly any chance for recovery. Especially if you have overwritten the data. The only chance is if you remember that you did a backup, for example using the "backupwallet" command.
The behaviour of the client is normal, it by default creates an entirely new wallet if none exists.