All round the room, have a double socket in each corner, then spaced at 2metre intervals or closer along the walls. You will want at least one at each side if the bed and at each side of a worktop or dressing table, at working height. You will need at least one where somebody might one day put a computer or TV.
The bedside and worktop ones might usefully have USB charging points in them
If they are more than 2 metres apart you will have gaps where you can't use an appliance without adding an extension lead, which is undesirable.
Because of the way UK power circuits are wired, it is possible, safe and economical to run the cable round the room with, effectively, an unlimited number of sockets on it.
The loft conversion should have its own lighting circuit, fused at 6A, and its own power circuit, fused at 32A. Both must be RCD protected, preferably individually on RCBOs so you will not be plunged into darkness if there is a trip. All this is easily done if included in the plan before work starts, but much more expensive to add later.