There are fears of possible clashes between military and civilian aircraft

There have been nine narrow escapes in four years, investigators say.

They are particularly concerned about repeated incidents over east Scotland, north east England and the North Sea.

The joint use of airspace by military and civilian planes needs urgent review, the Air Accidents Investigation Branch (AAIB) says.

There were two "extremely serious" incidents recently which would have resulted in "inevitable loss of life" had the aircraft collided, they say.

Of the nine incidents highlighted, the most recent was in February when an oil rig helicopter missed an RAF Tornado jet by just 50ft.

Use of unregulated airspace... should be reviewed jointly at the highest level by the CAA and MoD with the aim of eliminating... potential collisions Air Accidents Investigation Branch Catalogue of near misses

The AAIB report urges the Civil Aviation Authority to "re-examine the airspace categorisation, procedures and services currently available to Civil Air Transport aircraft...with the aim of ensuring that a level of protection is afforded to such aircraft from military aircraft".

It also calls on the Ministry of Defence to "ensure that procedures in use and the equipment fitted to military aircraft assure adequate separation of military aircraft from Civil Air Transport aircraft".

They should also undertake a joint review "at the highest level" of their shared use of unregulated airspace in the north east of the UK, the AAIB says.

It should be conducted "with the aim of eliminating airproxes [aircraft proximities] and potential collisions, with likely large scale loss of life," the AAIB said.

BBC Transport Correspondent Simon Montague said one solution to the problem would be to increase the regulated airspace around civilian airports.

However, the airspace above north east Britain is one of the few large areas left available for military training.

Any moves to increase controls around civilian airports would necessarily reduce the size of this training area, Mr Montague said.