Lofts in Burton Latimer split cleanly between the industrial era housing and the modern estates, and the two are genuinely different jobs.
On the older terraces the roofs are cut, with rafters and purlins, and the timbers were sized economically for a town building fast and cheaply. A conversion is often perfectly possible, but the structure usually needs strengthening rather than simply adapting, and where a previous owner has cut a purlin to fit a hatch or a water tank the roof has been quietly weakened. That gets found at the survey rather than when the new floor goes in.
On the modern estate housing, which is most of the town, the roofs are trussed. A trussed roof has no usable space until the structure is reworked, which means introducing new structure to carry the roof and the new floor independently before the redundant truss members come out. It is routine work and it is not the same job as opening up a cut roof.
Head height needs measuring either way, because floor build up and insulation take more out of a roof than anybody expects.
The permitted development volume allowance is forty cubic metres on a terrace and fifty on a semi or detached house, and on the estate plots a rear dormer inside that allowance is frequently achievable without an application. Escape, fire separation and stair position are Building Regulations matters. Our loft conversion page goes through the structural options.