diff --git a/docs/iris/src/whatsnew/latest.rst b/docs/iris/src/whatsnew/latest.rst
index a994a994e9..559d2483c1 100644
--- a/docs/iris/src/whatsnew/latest.rst
+++ b/docs/iris/src/whatsnew/latest.rst
@@ -126,6 +126,11 @@ Incompatible Changes
   Prior to Iris ``3.0.0``, these cases defaulted to ``units='1'``.
   See :pull:`3795`.
 
+* `Simon Peatman <https://github.com/SimonPeatman>`_ added attribute
+  ``var_name`` to coordinates created by the
+  :func:`iris.analysis.trajectory.interpolate` function.  This prevents
+  duplicate coordinate errors in certain circumstances.  (:pull:`3718`).
+
 
 Internal
 ========
diff --git a/lib/iris/analysis/trajectory.py b/lib/iris/analysis/trajectory.py
index 3a1f71a98b..d699b1c416 100644
--- a/lib/iris/analysis/trajectory.py
+++ b/lib/iris/analysis/trajectory.py
@@ -297,6 +297,7 @@ def interpolate(cube, sample_points, method=None):
             points = np.array([coord.points.flatten()[0]] * trajectory_size)
             new_coord = iris.coords.AuxCoord(
                 points,
+                var_name=coord.var_name,
                 standard_name=coord.standard_name,
                 long_name=coord.long_name,
                 units=coord.units,
diff --git a/lib/iris/tests/results/trajectory/tri_polar_latitude_slice.cml b/lib/iris/tests/results/trajectory/tri_polar_latitude_slice.cml
index 2224d12028..701ca7beb7 100644
--- a/lib/iris/tests/results/trajectory/tri_polar_latitude_slice.cml
+++ b/lib/iris/tests/results/trajectory/tri_polar_latitude_slice.cml
@@ -77,7 +77,7 @@
       </coord>
       <coord datadims="[2]">
         <auxCoord id="11ca7825" long_name="Latitude" points="[-78.1906, -78.1906, -78.1906, ..., 83.8392,
-		86.2794, 87.9471]" shape="(90,)" standard_name="latitude" units="Unit('degrees')" value_type="float32">
+		86.2794, 87.9471]" shape="(90,)" standard_name="latitude" units="Unit('degrees')" value_type="float32" var_name="nav_lat">
           <attributes>
             <attribute name="nav_model" value="Default grid"/>
             <attribute name="valid_max" value="89.6139"/>
@@ -87,7 +87,7 @@
       </coord>
       <coord datadims="[2]">
         <auxCoord id="ee0adb2e" long_name="Longitude" points="[-84.0002, -90.0001, -90.0001, ..., -86.9366,
-		-88.8945, -100.0]" shape="(90,)" standard_name="longitude" units="Unit('degrees')" value_type="float32">
+		-88.8945, -100.0]" shape="(90,)" standard_name="longitude" units="Unit('degrees')" value_type="float32" var_name="nav_lon">
           <attributes>
             <attribute name="nav_model" value="Default grid"/>
             <attribute name="valid_max" value="180.0"/>