I think @rehpot makes a very important point about bonds, equity income etc.
Some people might want to consider having funds in an investment grade fixed income fund something like, only for illustration purposes, PIMCO GIS Global Investment Grade Credit Fund Institutional GBP (Hedged) Income, IE00B3BMD843:GBP summary - FT.com.
In a pension situation you might want to take advantage of the 25% tax free lump sum*** - and do the cash conversion for that** when the market is going up rather than when the market is going down. Yup. Cash considerations are important.
**Of course you might choose not to do cash conversion for that and instead do a variation on what @weenie says where you take cash from dividends. Another alternative: you might decide you will liquidate a certain % of capital every year etc. It depends on what you decide the goals are (and inheritance may play a role here too).
*** Tax laws do change. So dunno if this one hangs around for ever.