Excellent time to let everyone know that I've just started a loft conversion business under a nationwide franchise Pinnacle Lofts. Fir a standard conversion with "proper" staircase no PP is needed but a Building Inspector will need to inspect a)when the floor goes in b)pre plaster & c) for a final completion certificate which will be needed when selling the property.
Be careful when choosing just on price paid as invariably you get what you pay for. (For example a non approved conversion could be only £5,000 but adds no value to your property!)
A good loft conversion company will manage the whole job including all project management & expect to pay £11,000 upwards......
However, when you weigh up the cost of moving home a conversion is very affordable
For more info on my company see
www.pinnaclelofts.co.uk