For a shotgun you do not have to give a reason to have, it is a right and you can have as many shotguns as you want as long as you can store them securely.
You complete the application form, referees forms and photograph and submit it with the fee. Eventually you will get an interview where they will check your security both the safe and the house.
I would advise against putting the safe in the loft. It's more awkward to get at so there's a tendency to "Put the gun away later" plus you are putting a lot more weight on the rafters which they may not have been designed for especially in a modern house.
As long as the safe is out of sight of visitors and secured properly to the wall it will pass inspection. If you can mount it in a corner with the opening (usually on the left) against the wall as this makes it more difficult to get a jemmy in.
If the FEO does ask what you are going to use the shotgun for just say clay shooting at various locations.
You don't say where in Staffordshire you live. If it's near Stoke the FEO is likely to be Brett Oakes. You might have to make your door frames higher as he's a bit tall - he has to duck coming through mine!
Offer him a cup of tea and answer any questions straight and you'll have no problems. You could mention that you intend to take lessons if asked.
Just remember when you fill the form in you have to declare any convictions and this includes any motoring offences which people tend to forget about.