Local aircraft controllers said they could not remember the last such time such a serious incident happened.
JLA immediately referred it to NATS which operates air traffic control for 15 of Britain’s largest air spaces.
NATS confirmed an independent investigation had been launched, but that 80% of aircraft separations were usually found to present no risk.
A spokeswoman said: “We can confirm there was a loss of separation on Monday 5 March at 2208 between two aircraft travelling to the north of Liverpool. The matter is now subject to an independent investigation.
It is understood the light aircraft was spotted by an onboard TCAS (Traffic Alert and Collision Avoidance System), and a separation monitor in the NATS control base.
A spokeswoman for Easyjet said: “We can confirm the flight EZY7254 from Krakow to Liverpool, operated by an Airbus 319 with 120 passengers and six crew, followed standard operating procedures and climbed to a slightly higher altitude, following notification on the aircraft's TCAS system that an aircraft a number of miles away had slightly exceeded the normal flying separation limits.
“At no time was safety compromised and this manoeuvre proves that the standard safety procedures in place are working exactly as they should, as both NATS and the Easyjet flight deck were aware immediately and took the appropriate steps.”
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