diff --git a/src/openflexure_microscope_server/scan_directories.py b/src/openflexure_microscope_server/scan_directories.py
index 3ef0c946..a8850afb 100644
--- a/src/openflexure_microscope_server/scan_directories.py
+++ b/src/openflexure_microscope_server/scan_directories.py
@@ -276,11 +276,15 @@ class ScanDirectoryManager:
         return [f.name for f in os.scandir(self._base_scan_dir) if f.is_dir()]
 
     @requires_lock
-    def all_scans_info(self) -> list[ScanInfo]:
+    def all_scans_info(self, ongoing: Optional[str] = None) -> list[ScanInfo]:
         """Return a lists of ScanInfo objects for each scan."""
         all_info: list[ScanInfo] = []
         for scan_name in self.all_scans:
-            all_info.append(ScanDirectory(scan_name, self.base_dir).scan_info())
+            # If the scan is ongoing send flag to skip reading the json data
+            skip_json = scan_name == ongoing
+            scan_dir = ScanDirectory(scan_name, self.base_dir)
+            info = scan_dir.scan_info(skip_json=skip_json)
+            all_info.append(info)
         return all_info
 
     @requires_lock
@@ -504,7 +508,7 @@ class ScanDirectory:
             LOGGER.warning(f"Could not validate scan data for {self.name}.")
             return None
 
-    def scan_info(self) -> ScanInfo:
+    def scan_info(self, skip_json: bool = False) -> ScanInfo:
         """Return the information to be used in the UI for the scan."""
         scan_files = self.get_scan_files()
         scan_images = self._extract_scan_images(scan_files)
@@ -514,7 +518,7 @@ class ScanDirectory:
         stitch_available = len(stitches) > 0
         dzi = None if not dzi_files else str(dzi_files[0])
 
-        scan_data = self.get_scan_data()
+        scan_data = None if skip_json else self.get_scan_data()
         duration = (
             None
             if scan_data is None or scan_data.duration is None
diff --git a/src/openflexure_microscope_server/things/smart_scan.py b/src/openflexure_microscope_server/things/smart_scan.py
index 0fc84f1c..c9454b11 100644
--- a/src/openflexure_microscope_server/things/smart_scan.py
+++ b/src/openflexure_microscope_server/things/smart_scan.py
@@ -588,6 +588,16 @@ class SmartScanThing(lt.Thing):
     )
     """Whether to run a final stitch at the end of a successful scan."""
 
+    def _get_all_scan_info(self) -> list[scan_directories.ScanInfo]:
+        """Return all the information from the scan directories.
+
+        It is preferable to use the method rather than calling
+        _scan_dir_manager.all_scans_info() directly as it will handle stopping the json
+        in any ongoing scans being read.
+        """
+        ongoing_name = None if self._ongoing_scan is None else self._ongoing_scan.name
+        return self._scan_dir_manager.all_scans_info(ongoing=ongoing_name)
+
     @lt.thing_property
     def scans(self) -> ScanListInfo:
         """All the available scans.
@@ -599,7 +609,7 @@ class SmartScanThing(lt.Thing):
         break it.
         """
         return ScanListInfo(
-            scans=self._scan_dir_manager.all_scans_info(),
+            scans=self._get_all_scan_info(),
             ongoing=None if self._ongoing_scan is None else self._ongoing_scan.name,
         )
 
@@ -667,7 +677,7 @@ class SmartScanThing(lt.Thing):
     def purge_empty_scans(self, logger: lt.deps.InvocationLogger) -> None:
         """Delete all scan folders containing no images at the top level."""
         # JSON is ignored as it's created before any images are captured
-        for scan_info in self._scan_dir_manager.all_scans_info():
+        for scan_info in self._get_all_scan_info():
             if scan_info.number_of_images == 0:
                 self._delete_scan(scan_info.name, logger)
 
@@ -791,6 +801,6 @@ class SmartScanThing(lt.Thing):
         """
         if self._scan_logger is not None:
             raise RuntimeError("Can't stitch previous scans while a scan is ongoing")
-        for scan in self._scan_dir_manager.all_scans_info():
+        for scan in self._get_all_scan_info():
             if scan.dzi is None:
                 self.stitch_scan(logger=logger, cancel=cancel, scan_name=scan.name)