Fetch XML link-entity attribute value

I have coded a fetch with a link-entity clause to get the value of an attribute in a related table that is working & returning the data I need [when tested using the XrmToolBox : FetchXml Tester tool].

The link-entity portion of the fetch statement is;-

"<link-entity name='new_ndisclientservice'  to='new_goalitem' from='new_supitemrefnum' link-type='inner' alias='SrvItm'> " +
         "<attribute name='new_costcentreid' />" +
"</link-entity>" +

When I run it in CRM using the XrmServiceToolkit, the FetchReturn.length = 2 (as I would expect on the basis of the criteria I am using) it is called via:-

var FetchReturn = XrmServiceToolkit.Soap.Fetch(FetchGoalNotes1Prsn(oFromDate, oToDate, oPrsnID));

So I know that the code is all OK up to that point. My issue is that when I try to get the value of  new_costcentreid  from the returned records the code stops running with no error message.

NB *  'new_costcentreid' is a look-up field in the 'new_ndisclientservice' entity.

To get the value of  new_costcentreid  I have tried various options including:-

  var oCostCentre1 = FetchReturn[0].Attributes["new_costcentreid"].value;

  var oCostCentre1 = FetchReturn[0].Attributes["new_costcentreid"].id;

I read another post that indicated that I needed to use the link alias so tried:-

  var oCostCentre1 = FetchReturn[0].Attributes["SrvItm.new_costcentreid"].value; 

 ..but that didn't work. Have tried a range of different ways but with no success - would appreciate any hints that may get this working.

Thanks in anticipation

Regards, Doug.