The guy from NATS interviewed on sky (sorry dont know his name) did say that no entity had put any pressure on them at all to re-open the airspace........ rather it was a decision that was made based on a better understanding of what is actually in the air based on all the data collected recently.
I guess the inference being........ more knowledge makes for more informed decisions. The position previously adopted was the ICAO NO ash is acceptable, but that was based on minimal, if any data. Now the various parties have data and have raised the bar from NO ASH to whatever ash now and im sure as time goes by that will be updated as well.