diff --git a/app/src/frontend/map/layers/city-base-map-layer.tsx b/app/src/frontend/map/layers/city-base-map-layer.tsx
index 315b7573..bfa58f4e 100644
--- a/app/src/frontend/map/layers/city-base-map-layer.tsx
+++ b/app/src/frontend/map/layers/city-base-map-layer.tsx
@@ -9,25 +9,30 @@ const OS_API_KEY = 'UVWEspgInusDKKYANE5bmyddoEmCSD4r';
  * Base raster layer for the map.
  * @param theme map theme
  */
-export function CityBaseMapLayer({theme}: {theme: MapTheme}) {
+export function CityBaseMapLayer({ theme }: { theme: MapTheme }) {
 
     /**
      * Ordnance Survey maps - UK / London specific
      * (replace with appropriate base map for other cities/countries)
      */
     const apiKey = OS_API_KEY;
-    const layer = theme === 'light' ? 'Light_3857' : 'Night 3857';
-    
+
+    // Note that OS APIs does not provide dark theme
+    const layer = 'Light_3857';
+
+    // In either theme case, we will use OS's light theme, but add our own filter
+    const theme_class = theme === 'light' ? "light-theme" : "night-theme";
+
     const baseUrl = `https://api.os.uk/maps/raster/v1/zxy/${layer}/{z}/{x}/{y}.png?key=${apiKey}`;
     const attribution = 'Building attribute data is © Colouring London contributors. Maps contain OS data © Crown copyright: OS Maps baselayers and building outlines. <a href=/ordnance-survey-licence.html>OS licence</a>';
-    
+
     return <TileLayer
-        key={theme} /* needed because TileLayer.key is not mutabe in react-leaflet v3 */
         url={baseUrl}
         attribution={attribution}
         maxNativeZoom={18}
         maxZoom={19}
         detectRetina={true}
+        className={theme_class}
     />;
 }
 
diff --git a/app/src/frontend/map/map.tsx b/app/src/frontend/map/map.tsx
index c2a3dda2..6df2bac4 100644
--- a/app/src/frontend/map/map.tsx
+++ b/app/src/frontend/map/map.tsx
@@ -144,7 +144,7 @@ export const ColouringMap : FC<ColouringMapProps> = ({
                         </div>
                     }
                     <Legend mapColourScaleDefinitions={categoryMapDefinitions} mapColourScale={mapColourScale} onMapColourScale={setMapColourScale}/>
-                    {/* <ThemeSwitcher onSubmit={this.themeSwitch} currentTheme={theme} /> */}
+                    <ThemeSwitcher onSubmit={themeSwitch} currentTheme={theme} />
                     <SearchBox onLocate={handleLocate} />
                 </>
             }
diff --git a/app/src/frontend/map/theme-switcher.css b/app/src/frontend/map/theme-switcher.css
index 19187414..eaa78dcb 100644
--- a/app/src/frontend/map/theme-switcher.css
+++ b/app/src/frontend/map/theme-switcher.css
@@ -1,3 +1,11 @@
+.night-theme {
+    filter: grayscale(100%) invert(1);
+}
+
+.light-theme {
+    filter: none;
+}
+
 .theme-switcher {
     z-index: 1000;
     position: absolute;