Procedure carried out was:
1. Check the search service and content account (sp_search newly created) had full read access to the web applications in Manage Web Applications -> Select each web application required to crawl and click administrator icon, in the popup check the search service account has read permission.
2. Check the search service account had read permissions on the content databases in SQL Server.
3. Disabled loop back security check on SharePoint Web Front End server which has the search service application installed on it, I used PowerShell and the following command:
New-ItemProperty HKLM:\System\CurrentControlSet\Control\Lsa -Name "DisableLoopbackCheck" -Value "1"
4. Added the hostnames used to the BackConnectionHostNames registry entry detailed in http://support.microsoft.com/kb/896861/en-gb. (make sure the FQDN and the aams are used.)