Empty the lot and only pay tax on it once at this year's rate rather than constantly paying tax on the annuity. Reinvest it post tax and you'll only pay tax on the gain, and then only when you draw it down...
Capital gains is significantly less than higher rate income tax.
That depends how much money is in the pot, and how much you currently earn from the day job. If it's (say) £20K then you can take £5K tax free and the other £15K at your current tax rate - so you would possibly only pay 20% tax on it (depends what other income you have this year).
However, if there is (say) £100K in the pot, then you can take £25K tax free, and the rest is taxable. You will pay 40% tax on at least some, and perhaps all of it - a tax bill of £30K.
If there is £1M in the pot, then £250K is tax free and the other £750K is taxable. You'll pay 45% on most of that - so you'll get a tax bill of up to £337K
.
The purpose of a pension is to provide you an income once you stop working. Taking taxable money out of the pension whilst you are still working means you will pay un-necessary tax. If you wait till you stop working then you'll have all of your personal tax allowance (£12K) and all of your 20% tax band (£38K) to withdraw the balance without pushing you into the 40/45% tax bands.
You don't have to buy an annuity any more, although they are still suitable for very risk averse people. There is (usually) no point in taking taxable money out of a pension to put it into investments. You can buy most investments inside the pension, and inside the pension they grow tax free and with no CGT.