Thanks to your help, your new combobox is now almost working in my project.
I have one tiny problem though. I have about 100 items to view so I thought I would just add a scrollbar with the following
telerik:RadComboBox x:Name="ddlCounty" scrollViewer.VerticalScrollBarVisibility="Auto" />
Sadly, the above line gives the following error
unknown attribute ScrollViewer.VerticalScrollBarVisibility on element RadComboBox
I am sure I have just done something wrong and there is another way of enabling scrolling.
Can someone please help me with this ?