From fb90a18c874e51d326522f508b306f83e81338f0 Mon Sep 17 00:00:00 2001
From: SimonPeatman <simon.peatman@sky.com>
Date: Sun, 24 May 2020 14:11:40 +0100
Subject: [PATCH 1/3] var_name in AuxCoord created by trajectory.interpolate()

---
 lib/iris/analysis/trajectory.py | 1 +
 1 file changed, 1 insertion(+)

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,

From 1b2ee4ed4b556a3fde919b0c484b767ed6943b18 Mon Sep 17 00:00:00 2001
From: SimonPeatman <simon.peatman@sky.com>
Date: Fri, 11 Sep 2020 12:03:26 +0100
Subject: [PATCH 2/3] Updated tri_polar_latitude_slice.cml

---
 .../tests/results/trajectory/tri_polar_latitude_slice.cml     | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

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"/>

From 8a0ddfaf38af58bf87ea7ef51cf7ddb78142279e Mon Sep 17 00:00:00 2001
From: SimonPeatman <simon.peatman@sky.com>
Date: Fri, 11 Sep 2020 21:31:21 +0100
Subject: [PATCH 3/3] What's New for #3718

---
 docs/iris/src/whatsnew/latest.rst | 5 +++++
 1 file changed, 5 insertions(+)

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
 ========