Checking how much all of your different pensions are worth is tricky, with most relying on their pension provider’s annual statement.

Those who do have online access to their pension may be forced to juggle passwords for a string of different schemes, as workers have on average eight different pensions over their lifetime.

No wonder many pensions end up going astray, typically after people forget to inform all of their pension companies when they lose move home.

Billions of pensions are lost, with the average value a staggering £13,000 each.

Many pension pots are difficult to manage.

Switching the underlying funds in the pension isn't easy and there may seem little point as pension providers may only offer a restricted choice of investment options.

Others have hefty charges, buried in the small print where they are hard to find and their impact impossible to calculate.

However, it is possible to tackle all of these issues and take full charge of you retirement savings by transferring them into something called a self-invested personal pension, or SIPP.

A SIPP is a DIY pension that offer a huge range of investments, including thousands of company shares and investment funds, plus bond funds, gold, property, cash and other assets.

They are sold by investment platforms such as AJ Bell, Bestinvest, Chelsea Financial Services, Hargreaves Lansdown and Interactive Investor, and stiff competition has driven down charges over the years.

SIPPs are usually free to set up and cost around £10 a month, plus trading charges of between £5 and £10 when buying or selling a stock or fund, and annual fees on any investment funds you hold.

Some providers offer cashback deals of £250 or more to encourage new customers.

With a SIPP, you are in control of your own pension, said Alice Haine, personal finance analyst at Bestinvest. “You can choose your shares or funds, while many platforms offer fully-managed investment portfolios for those who don't feel confident enough to do it themselves."

SIPP investors can pay in as little or as much as they want, provided they do not breach the pensions annual allowance, which is 100 percent of your income up to a maximum £60,000 a year.

As with any other pension, you can claim tax relief on contributions, 25 percent tax-free cash on withdrawals, and there's no inheritance tax bill when you die.

You can consolidating multiple existing pension pots into a SIPP, including old company pensions, Haine said. “If you are currently in a workplace pension with employer contributions, in most cases it will be best to leave that pension where it is. It can run alongside your SIPP.”

If you have lost track of any old pensions, contact the government’s free Pension Tracing Service which can help find them. They will need the names of your former employer or pension provider.

Before transferring, check you won’t sacrifice valuable benefits such as guaranteed annuity rates, terminal bonuses or extra tax-free cash entitlement, which may be available on some older schemes.

Watch out for exit penalties on your old pension plan, too.

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Be particularly wary of transferring out of final salary pensions or defined benefits schemes, where retirement income is linked to your earnings.

At retirement, you can take income in a way that suits you from age 55, whether via an annuity or drawdown.

As with any pension, you can pass unused SIPP holdings to loved ones free of inheritance tax and income tax if you die before the age of 75, said Andrew Tully, technical director at Canada Life. "If you die after 75, your beneficiaries may be liable to pay income tax on anything they draw from the pension.”

In a final advantage, if your pensions have been combined into a single SIPP, your beneficiaries won’t have the effort and uncertainty of tracking down multiple schemes.

SIPPs aren’t for everyone. Those with small pension schemes worth just tens of thousands of pounds may found the charges outweigh the savings.

Others may not want the bother of managing their investments.

In a SIPP, your income will depend on how well your investments perform. There are no guarantees and nobody to blame if stock markets crash.

That's the downside in managing your own money. It's certainly not for everyone.

If you need help, consider seeking independent financial advice or talking to the free Pension Wise service.