Someone showed me this yesterday and I thought it maybe of use for people who don’t have Memorymap or Anquet or lots of paper OS maps.
Goto Multimap. (http://www.multimap.co.uk) Ensure you select your country as United Kingdom if some other country is selected. Then position the map display to show the are of interest. Now, slide the zoom level slider to maximum. The display will be rubbish at this point. Click on the zoom out button (the minus sign) three times. Place your mouse cursor over the MAP button at the top left of the map display and leave it there. After a few seconds a small window to the right of the button will appear with an map image in it. Click on this and the entire map will be redrawn as a 1:50000 OS map.