There's a cap on the total value of all your pensions, which is currently £1.5 million. If the value of your pensions (including those in payment) exceeds the Lifetime Allowance when you take benefits or reach 75, you’re likely to incur a tax charge on the excess.
Important information - The pension and tax rules are subject to change by the government. Tax reliefs and state benefits referred to are those currently applying. Their value depends on your individual circumstances.