British Airways led the UK lobbying effort for a change in the way the risks of volcanic ash to aircraft are assessed.

So was it chief executive Willie Walsh who, more than anyone, secured a return to the sky following the ash crisis?

That is what BA chairman Martin Broughton has claimed, and there is some truth to the idea.

Certainly, a flight ban remained in force on Tuesday evening as Walsh joined other airline representatives, government ministers, Civil Aviation Authority officials and Nats air traffic control management to review the risk assessment that led to the ban.

Then at 8.44pm Nats issued a statement saying: “NATS has received new direction from the UK’s safety regulator, the CAA, on applying restrictions to UK airspace.” UK flights could resume from 10pm that night.

BA was among the first to welcome the ban’s lifting. But Walsh, like many other travel bosses, believes the measure was over-cautious. He said: “I don’t believe it was necessary to impose a blanket ban on all UK airspace.”

In reality, BA already had 26 aircraft heading for London before the ban was lifted. At least one had to be diverted to Brussels on being refused landing rights.

It is hard not to conclude this did not force the authorities’ hand, if only in speeding up the decision making. Restrictions had already been relaxed around much of Europe during the day, which meant the aircraft would be able to land somewhere.

BA refused to comment on Walsh’s role, other than a spokeswoman saying: “We have been very keen to get things moving. We have been very active.”

Other airlines and travel companies were every bit as frustrated, of course. Lufthansa described the restrictions as “scandalous” and Giovanni Bisignani, director general of airline association IATA, did not conceal his anger in a speech in Paris five days into the flight ban.

“In lost revenue alone, this is costing the industry at least $200 million a day,” he said. “We are far enough into the crisis to express our dissatisfaction on how governments have managed, with no risk assessment, no consultation, no coordination and no leadership. It is incredible it has taken five days for Europe’s transport ministers to organise a conference call.”

The initial relaxation of restrictions followed that conference call, which agreed a division of Europe’s airspace into a no-fly zone where the ash remains thick, corridors where flights can be permitted with restrictions, and open zones.

This, in turn, followed a new assessment of the risks following a series of test flights by major carriers at the weekend – including one by BA out over the Atlantic with Walsh aboard and others by Lufthansa and Air France-KLM.

These were initially dismissed as of limited scientific value by the CAA, which said: “They can’t collect data and they can’t actually tell you whether they flew through ash or not.”

Nonetheless, by Tuesday evening the CAA could announce: “The major barrier to resuming flights has been understanding tolerance levels of aircraft to ash. Manufacturers have now agreed to increased tolerance levels in low ash density areas.”

This followed, “new data collected from test flights and additional analysis from manufacturers over the past few days”.

So the ban was lifted. Presumably, as the dust settles we shall learn the extent to which evidence from the flights contributed to the change and to what extent the shift was due to expediency.

There are some outstanding issues for the industry, aside from the logistics of resumed operations and repatriation and the pursuit of compensation.

Two relate to aspects of the CAA’s Revised Airspace Guidance, which relaxed the ban but requires airlines to “conduct their own risk assessment . . . to address any remaining risks” and “put in place an intensive maintenance ash-damage inspection before and after each flight”.

BA insisted neither measure would complicate its operations nor increase the liability it already assumes. But lawyers might disagree on the latter and ground engineers on the former. Intensive “ash damage inspection” before and after each flight must occasionally compromise the airport turnaround time on a short hop, surely?

The impact on engines of repeated exposure to low levels of volcanic ash has also to be assessed. Returning to the sky may not be cost free if some aircraft subsequently require engine overhauls. One air safety consultant put the cost of repairing a new Boeing 747 damaged by ash at up $100 million.

And there is the question of who to blame for the hiatus in flying – if blame there must be. Many will point fingers at the government or the CAA or Nats. But the International Civil Aviation Organisation (ICAO), which seeks to standardise practices between the CAA and its equivalents worldwide, suggests the blame lies with the industry.

It told The Guardian the failure to agree a safe level of volcanic ash until now was because: “There is a huge liability issue for the [aviation] industry, so they have been super cautious in providing information.”