There is a property of the Association between the PEHorganisermaster and PEHcontract Domain Classes called IsManaged that can help you achieve what you what. When this property is set to True, the relationship between the navigation property newOrganiser.PEHcontacts and the actual contract objects is automatically maintained, meaning that when you add a new contract the Organiser_id property will be populated.
By default, the IsManaged property is set to False for all your associations for performance reasons, so you have to set it to True when you need this linkage automated for you.
Do not hesitate to let us know if you need any further clarifications on this.
the Telerik team