If your in a hypergrid enabled grid you can get to Britgrid by searching for http://britgrid.com:8002 in your viewers Map Find box.
If you've created an account at Britgrid and wish to set up your viewer to login to Britgrid directly, the following instructions may help.
Select Viewer, Preferences from the menu at the top left of the viewer window, select the Opensim option at the left of the Preferences window. Select the Grid Manager tab. In the Add new grid box type http://britgrid.com:8002 and then click the Apply button to the right and then The OK button at the bottom right of the window.
You should now be able to choose Britgrid from the Grid drop down options button at the bottom left of your viewers login screen. If no Grid button is available Choose form the top left menu Viewer - Preferences, select the Advanced button to the left of the window and put a tick in the box next to the Allow login to other grids (Not all grids will support Firestorm) option.
Choose Edit - Preferences then select the Grids button to the left of the window from the menu at the top left of the viewer login screen, or select the Grid Manager button at the bottom of the viewer login screen.
Select the Create Button then type http://britgrid.com:8002 in the Login URI: box, select OpenSim in the platform option and select the Apply and OK buttons at the bottom right of the window.
You should now be able to choose Britgrid from the Grid or Login URI: drop down button at the bottom left of your viewers login screen.