Loft Velux window escapes are no longer acceptable under ADB which now demands a protected route to the final exit.
However, I know of a case in a London Borough where the planning Dept insisted on a domestic sprinkler system for an identical problems (Victorian terraced house with a wall removed to make an 'open plan' design). The punters would have preferred a drop down fire curtain to create a virtual protected route, but the planners were obsessed with sprinklers
£8,500 worth of sprinkler later, the Boro Planners were happy and final cert was issued.
Mind you, as the system was installed merely to get 'permission' for the loft, the house owner has no plans to maintain the sprinklers and may actually disconnected them.
The householders reckoned that even with an £8,500 extra (unexpected) spend on the loft extension, with London prices, it's still much cheaper than moving
As so often with FS provision in dwellings, it's just an exercise - an example of red tape gone mad. As it's unenforceable, it's a complete waste of time and money which actually presents rise in risk for the householders.
It was the same with Velux windows in kids loft rooms (which were often locked) and self closers (I got mine third-hand for my loft extension and then passed them on).