Malaysia Airlines flight MH17 was flying just 1,000 feet (300 metres) above restricted airspace when it was shot down, according to the European air traffic control body.

Eurocontrol said Ukrainian authorities had barred aircraft from ground level to 32,000 feet but the doomed aircraft was cruising at 33,000 feet, still within range of sophisticated ground-to-air weaponry, when it was hit. All flights in eastern Ukraine have now been barred from the area, Eurocontrol added.

"The aircraft was flying at Flight Level 330 [approximately 10,000 metres/33,000 ft] when it disappeared from the radar," said. "This route had been closed by the Ukrainian authorities from ground to flight level 320 [32,000ft] but was open at the level at which the aircraft was flying."

It also emerged that as recently as a month ago British airlines were given the all-clear to overfly the area where flight MH17 was downed, after being told that operations were "normal" in the region.

A notice posted by the UK's Civil Aviation Authority (CAA) on 14 June urged carriers to avoid overflying Crimea and parts of southern Ukraine a month ago due to safety concerns, but they were not ordered to avoid the rest of the country.

Airlines were asked not to overfly Crimea, the Black Sea and the Sea of Azov due to the potential for conflicting air traffic control instructions between Ukrainian and Russian authorities. It added: "Operations are normal in all other Ukrainian FIRs [flight information regions]." However, the CAA notice added that UK airlines flying into the Dnepropetrovsk flight region, which includes Donetsk, should "review current security/threat information".

The CAA memo, known in the aviation industry as a Notice to Airmen or NOTAM, was broadly similar to a notice issued by the regulator's US counterpart in June. Neither of the Notams refer to a threat from ground-to-air missiles or fighter jets, with the CAA notice adding that a further safety review will be conducted by 1 August.

Before every long-haul flight, airline pilots are given clearance by the air traffic control bodies along their route. Once airborne, flights can still be rerouted for safety reasons by air traffic controllers as they enter a country's airspace so, in theory, the pilots of flight MH17 could have been warned by Ukrainian air traffic control of a threat from military forces on the ground more than 30,000ft below. International airlines submit flightplans to air traffic control authorities every six months or so. Major airlines such as BA also have risk advisers who inform pilots of risks involving specific territories such as Ukraine, on top of the Notams from the CAA.

In a statement the CAA said that after the MH17 disaster airlines had been told by the European air traffic control body to avoid the region: "The Ukrainian authorities are responsible for managing their airspace and the UK or other countries cannot enforce airspace restrictions in the area. However, the CAA has previously issued advice to UK airlines on operating in this area and following this incident, Eurocontrol has issued advice to airlines to plan routes that avoid the area."

The UK Department for Transport said airborne flights were now being rerouted around the area where MH17 crashed. "Flights already airborne are being routed around the area by air traffic control in the region."

Eurocontrol said flight restrictions were not in place for airspace at cruising altitude, where MH17 was hit.

A global airline industry group said on Thursday that MH17 appeared to have been flying through ordinary and open airspace when it crashed.

"Based on the information currently available, it is believed that the airspace that the aircraft was traversing was not subject to restrictions," said the International Air Transport Association.

British Airways said it was not overflying Ukraine. "The safety and security of our customers is always our top priority. Our flights are not using Ukrainian airspace, with the exception of our once-a-day service between Heathrow and Kiev. We are keeping those services under review, but Kiev is several hundred kilometres from the incident site."

Germany's Lufthansa said it had decided to avoid east Ukrainian airspace with immediate effect, while Russia's Transaero said it would avoid Ukraine altogether and Reuters reported that Emirates had suspended flights to Ukraine. In France, a statement by the junior transport minister Frédéric Cuvillier said he had advised French airlines "to avoid Ukraine's airspace as long as the reasons behind this catastrophe are not known."

A pilot for a major European airline who has flown over Ukraine since the conflict began said it was normal practice for airlines to fly over conflict zones. "We would often avoid areas where there is air-to-air conflict, but we flew over Iraq and Afghanistan when the British and US armed forces were deployed there, because only one side was using military jets."

Explaining why airlines fly over conflict zones, where groups might be in possession of ground-to-air missiles, the pilot said: "There will be weapons based on the ground when you are at 30,000 feet, but that is far up in the air. There are not many missile systems that can be so accurate."

The pilot added that hand-held missile systems were not viewed as a threat to airlines flying at altitude but sophisticated weaponry, such as the Buk system that has been cited as being involved in the MH17 disaster, was much more dangerous. Had-held rocket launchers have been used against commercial aircraft, including an attack in Kenya in 2002 when a shoulder-launched missile just missed an Israeli airliner during take-off at Mombassa airport. In 2003 army vehicles and 1,500 anti-terrorist police were deployed at Heathrow amid fears of a similar attack.

The pilot's comments indicate that assumptions about flying over conflict zones where groups are known to be armed with ground-to-air missiles will now have to be reviewed. However, the pilot added that Ukrainian airspace was regularly overflown by European airlines – including British Airways, Lufthansa and KLM – and imposing a no-fly zone over the entire country would have commercial and logistical consequences for carriers.

"Ukraine is huge. If you were to close that airspace it would be a long way round for a lot of airlines. If you were to close it to high-level traffic it would be quite expensive in terms of extra fuel and it would be quite disruptive."

The cost of airspace restrictions was made clear to European airlines in 2010 and 2011 when an Icelandic volcano erupted and forced jets to be grounded across the continent, costing airlines millions of pounds in compensation and lost revenues and disrupting the travel plans of millions of people.