Old town would be a good option - try the High Rise http://www.old-town.co.uk/products/highrise.htm , or if you want something a little more casual, the Orfords - http://www.old-town.co.uk/products/orfords.htm
If you're not too strict about them being white-white, and would be happy with an off-white, or "Old English White", try these: http://www.ebay.co.uk/itm/WW2-Germa...5?pt=US_CSA_MC_Pants&var=&hash=item9c027b4233
These are my pair in use (I'm considering a second pair for this Summer). Absolutely fine for casual wear (which this sort of thing mostly is):
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