In reply to FlapsOne's entry of 2/9/01.
If you are going to miss your slot because of an unforeseen problem at an airfield, ATC at that airfield are obliged to call Flow for a new slot (or an extension to the existing slot).
We then have a number of options.
We check the load in the critical sectors, if there is room we agree to the extension. If there is no room, we can still agree to the extension and move another flight in the affected sector to a different slot (by swapping to your old slot for example).
In exceptional cases where there is a load problem in the sectors involved (too many flights) or its too late to move any of the other flights in the sector (already airborne for example)we may have to refuse the slot extension, but that really is a last resort, after all missed slots are wasted slots.
To answer your question, the point of the slot in the first place was to protect ATC from overdelivery of traffic- that's dangerous. The reason you can still go anyway even though you've missed the original slot is because the faceless bastards in the background (like me) are beavering away to try and make the whole thing run smoothly.
If you prefer we can send you back to stand to wait for another slot, but I don't think that will make you feel any better (or us).