The owner of a sick horse that had to be euthanased after being spooked by a low-flying Virgin hot air balloon is writing to Sir Richard Branson about the incident.

Liz Jones’ 18-year-old mare Della was being treated for equine herpes (EHV-1) when the balloon flew low over her field at Friar Park Stables in Henley, Oxon, on 10 August. The pilot had just aborted a landing at the town’s rugby club.

Mrs Jones said there was a “massive roar” and flames as the pilot put the burners on. Della tried to bolt, but fell to the ground. She was unable to get up and was put to sleep.

“The vet had seen some improvement [in her symptoms] and said if she could make it through the night, there was a chance,” said Mrs Jones.

She is mystified as to how Della contracted EHV-1, as she does not compete the mare, bought for her daughter Kathryn who is now at university. Quarantine procedures are in place at the yard.

“I’m writing to Mr Branson’s office to say that his pilots should not be flying that low. I want to draw pilots’ attention to livestock below and to be careful around horses,” said Mrs Jones.

A spokesman for Virgin said they were “truly sorry” to hear about the loss of Della, but they did not believe that the pilot — who has 30 years’ experience — had been irresponsible.

The area has been used for balloon landings and launches for seven years “without an issue”, he added.

“All balloon pilots are trained to consider the welfare of livestock. In this case, it appears that an unfortunate set of circumstances, including the fact the horse was unwell, culminated in this very sad outcome.”

The yard has now been marked as a “sensitive area” on ballooning maps.

Earlier this year, it emerged that Virgin settled an injury claim, after one of its hot air balloons spooked a horse in Cambridgeshire, injuring itself and its teenager handler.