Monty Gordo RE BHX RUNWAY.
Runway 15 has a threshold elevation of 303 feet above sea level and runway 33 being 326 feet.
As Invicta says a few hundred feet makes little difference, perhaps 30 metres over a sea level airport.
However if you look at some airports.. Calgary for example, its 3,600 feet about sea level, so the airs thinner and more speed and lift needed to reach "V" for airliners.
Some airports also are very high and very hot, the heat further thinning the air requiring even longer take off distances.
Attach NATS latest BHX chart of BHX where you can see the heights..
http://www.ead.eurocontrol.int/eadba...2012-05-03.pdf
Nigel