on Mondays to Fridays, outside the period 0630 to 0930 and 1630 to 1930 , I doubt there's lots of holding taking place. MAN was operating around 45 movements an hour on 1 runway and I was there on a couple of occasions when 50+ was achieved.... but that was peak period in the summer.
Having 2 runways cater for 30 movements an hour from 1200 to 1500 doesn't make sense. But if easyJet do go to 10 based aircraft by 2012, there's the potential for 8 more movments in the "dead" period. Similar possiblities occur for airlines like Monarch and Jet2
With the availability to charge less in the off-peak period, it may be possible for some of the lost routes to come back or some of the incumbent airlines to consider them by non-MAN based aircraft.