Right, i've fixed it without the need to do the reg clean as Dev suggested (although this does need to be done at some point).
The fix was rather simple as it turned out... I uninstalled reporting services and attempted to reinstall it. I got an error that said:
"The SQL Server instance MSSQLSERVER already has an instance id 4 that is different than the specified instance of MSSQLSERVER. Specifying more than one instance ID for the same SQL Server instance is not supported."
This appeared before the feature selection screen so i was stuck. Jumped on google and found this link
i deleted the reg key for Instance ID 4 because that was the incorrect one ie. HKLM\SOFTWARE\Microsoft\Microsoft SQL Server\Instance Name\RS.
When i then tried to the add features to an existing install option again i was able to install reporting services on it's own selecting manual configuration. Once that compelted 5 minutes later i'd configured reporting services and it's all working sweet as a nut. :-)
Thanks for your help Perry/Dev. Hopefully someone else will find this thread useful in the future....
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