If you want to have your cask ale last longer, (I know, I know, not "real"), carb it to 1.1 volumes in a corny, (with priming sugar, if you like). Then, cool it to 12-13*C, (52-55*F), wait a day, vent any excess pressure, and use a CO2 breather to provide atmospheric CO2 to replace the beer as you draw it off. Beer can last as long as normal kegged beer in this case, but still have that "Real Ale" quality of low carb, warm temp. You can even pull a few pints from it at first without the breather, then attach the breather, to get just enough O2 in there to give that bit of oxidation that Real Ale would have.
If you don't want to shell out for a real breather, you can use a propane regulator for a propane grill....it regulates down to 11"WC, IIRC, which is pretty much atmospheric, (enough pressure to push water up a pipe 11" inches, or about 0.5 PSI).