When I met Jon Squirrell of the Vault Gym for the first time in November 2012 I faced him with a challenge. Having bid for and won a charity place to run in the Virgin London Marathon 2013 (together with programme and training sessions at the Vault), I arrived at the gym with serious misgivings and fully prepared to tell Jon it had all been a big mistake. To run a marathon had been a dream of mine for a number of years but something I had lacked the confidence to undertake.

Not quick to present his point of view, Jon listened to me with grace and an open mind. My question was that, since I wasn't fit enough, nor could I pound the streets six days a week, could I train for a marathon without actually running? Jon heard what I had to say but saw the potential. We chatted through the options for a while, his calm and gentle manner assuring me that there may just be a way through. I accepted the invitation to put on my gym gear and, to quote Jon, “put my life in his hands”. After an hour's circuit session, I left the gym that day not only determined to run a marathon but announcing that I wanted to do it in under four hours.

Jon inspired me with confidence from the outset. We worked hard from day one but had fun. His own athletic experience and expertise meant that he was able to create a programme for me which was individual and incredibly effective. A mix of home-based bodyweight workouts, treadmill sessions and outdoor runs was complemented by full-on circuits in the gym consisting of everything from boxing to weightlifting and much, much more. We hit a track for speed sessions, Greenwich Park for the hills. Never dull and with targets that were achievable, determination and hard work saw progress made. Jon's integrity and client service throughout was second to none. My phone calls were returned, often late in the evening, and programmes emailed through without delay. His attention to detail and customer care were exceptional. On April 21st 2013, I achieved my goal of running a marathon in under four hours. I am deeply grateful to Jon for his expertise in creating a programme for me which worked to perfection and for his time and friendship along the way .

Jon is a man who displays a rare mix of natural giftedness, business vision and a heart for people all of which inspires and encourages others to achieve.

Jon Squirrell is one of a number of personal trainers I have used over 20 years in London. Most lost their dedication and mission aim within a year of me joining them. Jon is quite different. He has the hallmark of a good trainer. This for me is a consistent high standard of personal care and training month in, month out, no wobbles, no absences, and no drama. I wanted to keep achieving a higher and higher standard of fitness. Both his engaging personality and his dedicated maintenance of my own goals achieved this. For me, he is quite simply the best.

Seven years ago after the birth of my second son I set out to find a personal trainer. Having worked for Nike in the fitness industry for some years I was quite exact about the calibre of trainer I wanted. Jon came recommended from a reliable source in the fitness industry and so our work-out journey started. Back then, I was a training snob and didn't really believe an hour once a week could make a difference. Jon proved me wrong.

He exceeded my expectations in terms of professionalism, knowledge and most importantly the ability to keep workouts fun and challenging. He has a natural intelligence that shines through his work and, as I await the arrival of my third son, I am reminded of what safe hands I am in and I can enjoy exercising up until the birth.

Jon Squirrell is an excellent coach. Having trained with him for more than a decade, I've seen great results. Jon's solid methodology and no-nonsense approach has always been a breath of fresh air in an industry dominated by fads and needless expense. I could not recommend a better guy to get you back in the game.

I have a better body at 40 than I did at 20. And that's with just two sessions with Jon a week, and not much constraint on the sauvignon blanc and munchies.

It feels deceptively easy, but he works you hard and the results are very quick. Somehow Jon knows my limits better than I do – I have surprised myself with what I can do and love being back in skinny jeans.

It doesn't seem quite right that just 2-3 sessions a week should make so much difference. I still eat whatever I want but I am in better shape than ever. The man is a genius!

Dear Jon,
I wanted to thank you for your advice on managing my diet to help with my MS, and update you on my progress.

I started with the new regime five months ago, upping my fruit and vegetable intake  – specifically greens and bright coloured fruits, oily fish and reducing caffeine. Since then I have noticed improvements in my concentration and ability to focus on conversations and discussions (which I had been finding more difficult) and my energy levels have improved. Also, results from a recent MRI scan showed there were fewer lesions since the last MRI compared to the previous years and I am convinced the change in diet is a major contributor to this.

I have been training with Jon for three years, starting when I was 40. Before then I did not go to a gym. I found the odd trip to a hotel gym boring and the equipment off-putting. Over the past three years, seeing him on a weekly basis, he has changed my body. I am fitter and stronger at the age of 43 than I have ever been. I weigh less than I did 10 years ago, and that's without cutting back too much on the beer and chips.

I think one of Jon's great talents is his understanding of his clients, and their strengths and weaknesses. I was a reasonably strong runner, but otherwise did not work out. Jon helped me to get into weight bearing exercises and core training. This was all done in a way that challenged me, but wasn’t daunting.

Jon also has very good technical knowledge. The various exercises are planned to complement each other. He is also a nice easygoing guy. My work can sometimes be quite stressful. I look forward to having a session with him. It is a great way to blow away the stresses of the day job.

Jon provides a good service. He is reliable and easy to get in touch with. He is also flexible in accommodating the demands my work sometimes makes on my evenings. He has done a great job at the Vault Gym. It is an excellent gym and I know how much work he puts into keeping it that way.

Jon has trained me since 2006. I started going to him because I wanted a trainer with a competitive sports background to help get me fit for a sailing Masters World Championships (Jon’s background is in elite athletics (400 metres)). He has trained me ever since and got me ready for six Masters Worlds. Jon is super-professional and knowledgeable, but also has a very easygoing approach and is fun to spend time with. The workouts are tailored to whatever I am trying to achieve – in my case, general all round fitness with an aerobic emphasis and are really fun, with plenty of variety. Even after seven years, he is still introducing exercises I've never done before. He’s a fantastic motivator and it’s hard to imagine that there is a better trainer out there.

In a year and a half of training with Jon, I’ve lost a stone, gained muscle tone and, crucially, recently won my first ever running race. Granted, it was a dad’s 100m sprint at my daughter’s school sports day but, as someone who has never won a race in my life, coming first at this in front of my daughter felt amazing. My work with Jon at The Vault (brilliant gym, by the way), combined with weekly sprint sessions at a local running track, has – at the age of 44 – given me a fitness level I could only dream of. Still not used to those 6am starts though!