One server with a Dual Core processor.

 I think I have managed to improve the problem slightly by setting the caching mode from Heavy to Moderate. This did not make any difference in V4 but in V5 it seems to have helped.

It turns out I had a web garden which I did not know about. The worker processes was set to 4. The grass must have got very long but now its all gone and the website seems to behaving better for it.

Now I know the keyword web garden it appears I am not the only one to have fallen into this trap.

Thank you so much for your help" For those who find this post in future, here is how you get rid of your web garden.

To change IIS, follow these steps:

1. Click Start -> Administrative Tools -> Computer Management.
2. Expand "Services and Applications", then "Internet Information Services", and then "Application Pools"
3. Locate the Application Pool Secret Server is running as. To determine this, Expand "Websites", then the Website Server Server is running on. Find the Virtual Directory (if it is running on one) and click Properties. The "Home Directory" tab will indicate Secret Server's Application Pool.
4. Right click the Application Pool, and click "Properties". You should now be on the "Recycling" tab.
5. Select the performance tab.
6. Set the "Maximum number of worker processes" to 1.