Well, right now, today, a perfectly safe option is to put it into a guaranteed investment like the NS&I 6.2% bond.
If you started with the million quid limit and could choose that option year upon year, then you can afford a draw down of £62k a year and you won't run out of money.
Other more complicated options are available.
You can build a fairly simple spreadsheet to model a starting amount against all scenarios over time, because that option very probably won't always be there for the rest of your life.