Good advice here- the Council (and Landlord for that matter!) will be able to confirm the Planning Use given to this building. It is probably Offices which means you may have trouble. I have copied this from the Planning Portal website,
Use classes order
The following classes of use for England are set out in the Town and Country Planning (Use Classes) Order 1987 and its subsequent amendments.
A1 Shops - Shops, retail warehouses, hairdressers, undertakers, travel and ticket agencies, post offices, pet shops, sandwich bars, showrooms, domestic hire shops, dry cleaners and funeral directors.
A2 Financial and professional services - Banks, building societies, estate and employment agencies, professional and financial services and betting offices.
A3 Restaurants and cafés - For the sale of food and drink for consumption on the premises - restaurants, snack bars and cafes.
A4 Drinking establishments - Public houses, wine bars or other drinking establishments (but not a night clubs).
A5 Hot food takeaways - For the sale of hot food for consumption off the premises.
Your solicitor also needs to establish if you are having a lease in your own right (i.e. from the Landlord) or you are taking a sub-let from one of the offices (in which case the Landlord must also consent)