Tina Cook has already accomplished arguably the greatest feat of her eventing career - whatever happens at London 2012.

In just 15 days' time, Cook and the rest of Great Britain's Olympic team - William Fox-Pitt, Mary King, Zara Phillips and Nicola Wilson - will begin their medal bid at Greenwich Park.

But for 41-year-old Cook and her London horse Miners Frolic such an exciting scenario could not even have been contemplated 12 months ago.

While some of her international colleagues prepared for the Olympic Test event in Greenwich, Cook could only hope and pray that Miners Frolic would pull through a life-threatening illness.

Cook had won two Olympic bronze medals and the 2009 European individual title on 'Henry,' but those memorable highs were temporarily engulfed by feelings of utter despair.

So when one of British eventing's most successful combinations in recent years head into the Greenwich Park dresssage arena later this month, mission improbable will have been accomplished.

''The vets didn't think he would live,'' said Cook, recalling the day when Miners Frolic was hit by colitis, which is an inflammation of the colon.

''Only 50% of horses survive it. He was on a permanent drip, had very high levels of toxins in his blood and was hallucinating.

''I thought that was it. He was very, very ill. It would have been an awful way for any horse to go, let alone one who has done as much for me as he has.

''I felt so helpless. I had never been involved in anything like it. He was totally in the vets' hands.''

Miners Frolic was treated at Arundel Equine Hospital in Sussex, and after a week in intensive care his condition stabilised and he was allowed home to Cook's yard.

Several weeks elapsed before he was able to do light work with Cook, and then after a spell convalescing with his owners in Wiltshire, he returned last October as his rider faced some big decisions.

Because Miners Frolic missed all last season's key competitions - including Badminton due to a lump on his withers that took six weeks to heal - he had not secured Olympic qualification.

So Cook opted for an early-season run at Ballindenisk in Ireland, with that qualifying target the aim.

''When he came back to me from his owners, he looked wonderful, like a show horse,'' she added.

''Outwardly, he looked good and he felt good, but we had no idea how much damage had been done to his insides.

''I wasn't at all sure what to expect, and I was fully prepared not to run him at Ballindenisk if the ground was too soft. It was soft, but the organisers there had done a brilliant job with it and with the cross-country track.

''I wasn't sure about Henry's fitness and I hadn't wanted to put him under too much pressure beforehand as he is quite sensitive and a bit of a worrier.

''But he felt amazing and was full of running after nine minutes across country, which was the objective.''

Olympic qualification was secured with a third-place finish, and after a strong display at the Bramham International Yorkshire five weeks ago, London selection was secured.

Whether or not Cook and Miners Frolic can now enhance their impressive list of achievements - Olympic team and individual bronze, European individual and team gold, world team gold - remains to be seen, but just being in London represents a Herculean achievement.

''To be selected for the Games is a dream come true,'' she said.

''With his past form, Miners Frolic has proved he can do it, but he nearly died of colitis 12 months ago, so to come back to this level shows he is a real fighter.

''I am very excited to get the opportunity to take him to London.

''Nothing could have been further from my mind than the Olympics when he was so ill. I just wanted him to live.''