You will also need the 2 letter grid reference. Wales uses SH, SJ, SM, SN, SO, SR, SS, ST. Streetmap.co.uk allows a search using os grid references eg: SN694599
As others have indicated, the grid reference you provided isn't unique, as it will occur within every grid reference square in the UK. You need to precede it with the appropriate pair of letters. See here:
http://www.sewhgpgc.co.uk/images/ukos.gif
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