Despite what noseall says, that is not correct. Building Control will look at what the room could potentially be used for, not what you say it is being used for. For example, say you sell the property, the new owner thinks "this is a nice little loft room, ill make this my daughters bedroom" the daughter then burns to death when a fire occurs because adequate means of warning and escape have not been allowed for. I myself work in the building control proffesion, and we have plenty of people who claim to be doing work to their loft for 'storage' purposes. Most Building Control surveyors are not daft, and know exactly what the deal is with this kind of work and usually advise people accordingly. Just dont be suprised when you come to sell your property if your solicitor starts asking arkward questions about your loft 'storeroom' and requesting copies of Building Regulations approvals!!!
The trouble with everything you've just stated is
No just a new drop down hatch and fitted loft ladder.