diff --git a/base/uk.ac.stfc.isis.ibex.ui.configserver/src/uk/ac/stfc/isis/ibex/ui/configserver/editing/blocks/BlockDetailsPanel.java b/base/uk.ac.stfc.isis.ibex.ui.configserver/src/uk/ac/stfc/isis/ibex/ui/configserver/editing/blocks/BlockDetailsPanel.java
index 8037c524f4..87efb60e67 100644
--- a/base/uk.ac.stfc.isis.ibex.ui.configserver/src/uk/ac/stfc/isis/ibex/ui/configserver/editing/blocks/BlockDetailsPanel.java
+++ b/base/uk.ac.stfc.isis.ibex.ui.configserver/src/uk/ac/stfc/isis/ibex/ui/configserver/editing/blocks/BlockDetailsPanel.java
@@ -31,6 +31,9 @@
 import org.eclipse.swt.widgets.Group;
 import org.eclipse.swt.widgets.Label;
 import org.eclipse.swt.widgets.Text;
+import org.eclipse.swt.custom.StyledText;
+import org.eclipse.swt.graphics.Color;
+import org.eclipse.swt.custom.StyleRange;
 
 import uk.ac.stfc.isis.ibex.ui.widgets.buttons.IBEXButton;
 
@@ -42,11 +45,14 @@
 public class BlockDetailsPanel extends Composite {
 	
 	private final Text name;
-	private final Text pvAddress;
+	private final StyledText pvAddress;
 	private final Button visible;
 	private final Button local;
 	private final Button btnPickPV;
 
+	private final Color prefixColor = new Color(getDisplay(), 166,28,0);
+	private final Color prefixHighlight = new Color(getDisplay(), 244, 204, 204);
+	
 	/**
      * Standard constructor.
      * 
@@ -85,10 +91,13 @@ public BlockDetailsPanel(Composite parent, int style, final BlockDetailsViewMode
 		lblPvAddress.setLayoutData(new GridData(SWT.RIGHT, SWT.CENTER, false, false, 1, 1));
 		lblPvAddress.setText("PV address:");
 		
-		pvAddress = new Text(grpBlock, SWT.BORDER);
+		pvAddress = new StyledText(grpBlock, SWT.BORDER);
 		GridData gdPvAddress = new GridData(SWT.CENTER, SWT.CENTER, true, false, 2, 1);
 		gdPvAddress.minimumWidth = 380;
 		pvAddress.setLayoutData(gdPvAddress);
+		pvAddress.addExtendedModifyListener(e->updateStyle(viewModel.getPrefix()));
+				
+		
 		
 		btnPickPV = new IBEXButton(grpBlock, SWT.NONE, _ -> viewModel.openPvDialog())
 				.layoutData(new GridData(SWT.LEFT, SWT.CENTER, true, false, 1, 1))
@@ -98,6 +107,21 @@ public BlockDetailsPanel(Composite parent, int style, final BlockDetailsViewMode
 		setModel(viewModel);
 	}
 	
+	
+	
+	private void updateStyle(String prefix) {
+		StyleRange prefixStyle = new StyleRange();
+		prefixStyle.start = 0;
+		prefixStyle.length = prefix.length();
+		prefixStyle.foreground = prefixColor;
+		prefixStyle.fontStyle = SWT.ITALIC;
+		prefixStyle.background = prefixHighlight;
+		if (pvAddress.getText().startsWith(prefix)){
+			pvAddress.setStyleRange(prefixStyle);
+		}
+	}
+	
+	
 	private void setModel(BlockDetailsViewModel viewModel) {
 		DataBindingContext bindingContext = new DataBindingContext();
 		
@@ -122,4 +146,5 @@ private void setModel(BlockDetailsViewModel viewModel) {
                 BeanProperties.value("visible").observe(viewModel));
         
 	}
+	
 }
diff --git a/base/uk.ac.stfc.isis.ibex.ui.configserver/src/uk/ac/stfc/isis/ibex/ui/configserver/editing/blocks/BlockDetailsViewModel.java b/base/uk.ac.stfc.isis.ibex.ui.configserver/src/uk/ac/stfc/isis/ibex/ui/configserver/editing/blocks/BlockDetailsViewModel.java
index 870293bc94..0c009a290c 100644
--- a/base/uk.ac.stfc.isis.ibex.ui.configserver/src/uk/ac/stfc/isis/ibex/ui/configserver/editing/blocks/BlockDetailsViewModel.java
+++ b/base/uk.ac.stfc.isis.ibex.ui.configserver/src/uk/ac/stfc/isis/ibex/ui/configserver/editing/blocks/BlockDetailsViewModel.java
@@ -29,6 +29,7 @@
 import uk.ac.stfc.isis.ibex.configserver.editing.BlockNameValidator;
 import uk.ac.stfc.isis.ibex.configserver.editing.EditableBlock;
 import uk.ac.stfc.isis.ibex.configserver.editing.EditableConfiguration;
+import uk.ac.stfc.isis.ibex.instrument.Instrument;
 import uk.ac.stfc.isis.ibex.ui.configserver.dialogs.PvSelectorDialog;
 import uk.ac.stfc.isis.ibex.validators.ErrorMessageProvider;
 import uk.ac.stfc.isis.ibex.validators.PvValidator;
@@ -48,6 +49,8 @@ public class BlockDetailsViewModel extends ErrorMessageProvider {
     private final EditableConfiguration config;
     
     private final List<String> facilityPvList;
+    
+    
 
     /**
      * Constructor.
@@ -150,8 +153,26 @@ public boolean isLocal() {
      * @param local true for local
      */
 	public void setLocal(boolean local) {
+		String prefix = Instrument.getInstance().getPvPrefix();
+		String pvAddress1 = pvAddress;
+		if (local) {
+			if (!pvAddress.startsWith(prefix)) {
+				pvAddress = prefix + pvAddress;
+			}
+		}else {
+			if (pvAddress.startsWith(prefix)) {
+				pvAddress = pvAddress.substring(prefix.length());
+			}
+		}
 		firePropertyChange("local", this.local, this.local = local);
+		firePropertyChange("pvAddress", pvAddress1, pvAddress);
+	}
+	
+	public String getPrefix() {
+		return Instrument.getInstance().getPvPrefix();
 	}
+
+	
     
     /**
      * Open the PV dialog window.
@@ -169,7 +190,6 @@ public void openPvDialog() {
     public void updateBlock() {
     	editingBlock.setName(name);
     	editingBlock.setPV(pvAddress);
-
     	editingBlock.setIsLocal(local);
     	editingBlock.setIsVisible(visible);
     }