The median age for SIPP millionaires is 62, according to Hargreaves Lansdown which analysed its data from its 3,166 SIPP millionaires.

When asked how they got to the million pound point with their SIPP, the most popular answer was how important it was to start contributing to a pension as early as possible and increase contributions on a regular basis.

The majority of Hargreaves Lansdown’s SIPP millionaires were no longer contributing to their pensions, with those still contributing doing so on an ad-hoc basis rather than making regular contributions.

The lifetime allowance is the largest current barrier to becoming a SIPP millionaire according to Helen Morrissey, senior pensions and retirement analyst at Hargreaves Lansdown.

She said: “It takes years of regular saving to build up such a pension but these millionaires show it can be done. Auto-enrolment should boost the number of people able to reach this important milestone in the coming years as we see more people contributing throughout their entire careers.

“There are issues to be aware of though. The current lifetime allowance currently stands at £1,073,100. Pensions worth more than this will attract a tax charge. This does not necessarily mean you should stop contributing to a pension if you hit the limit but it’s probably worth discussing your options with a financial adviser.

“Some of these millionaires will have accumulated their wealth at a time when the lifetime allowance was higher and will have organised protection for their pensions when it was decreased. Not so long ago it was as high as £1.8m."

The SIPP millionaires questioned by Hargreaves Lansdown also said it was important not to chase short-term fads and fashions in in the hope of ‘making a quick buck’.

The millionaires also advocated taking time to understand what the SIPP is invested in and getting to grips with pension tax treatment.

Several also noted that making retirement income decisions was complex and that speaking to a financial adviser was always a good option.