The Government has set a limit on the amount that you can have in all forms of pension you hold, which for 2014/15 is £1.25m.
Every time you take benefits from your pension, you crystallise that proportion, and the relevant portion of your lifetime allowance is used up. If you reach age 75 without securing an income via an annuity you will also have your benefits tested against the lifetime allowance. If you have had more in total than the £1.25m limit, you will face the lifetime allowance charge. Please remember that tax limits can change in the future.