The Air Accidents Investigation Branch said the banner became wrapped around the plane A plane crash in which UKIP leader Nigel Farage and his pilot were injured was caused when an election banner became entangled in the tail fin.
The aircraft came down shortly after taking off from Hinton-in-the Hedges airfield in Northamptonshire on 6 May – election day.
Mr Farage, 46, and pilot Justin Adams were seriously injured.
An Air Accidents Investigation Branch (AAIB) report said the towed banner caused the plane’s nose to drop.
Although Mr Adams “maintained some control of the aircraft” he could not prevent it crashing, the report said.
Mr Farage suffered broken ribs, bruised lungs and facial injuries, while Mr Adams was trapped in the wreckage of the aircraft and also needed hospital treatment.
Mr Farage had been campaigning against Commons Speaker John Bercow for the constituency of Buckingham. Mr Bercow later won the seat.
The AAIB said the aircraft had taken off with Mr Farage in the passenger seat “intending to receive text messages from colleagues on the ground giving locations where the banner could be shown to maximum effect”.
Previously Mr Farage said the worst part was being trapped in the plane as petrol poured over his clothes and hair.
“I thought: ‘God, we survived the impact, now we’re going to burn to death’,” he said.
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