Any commercial insurance policy that is designed to, amongst other covers, insure assets, ie building, contents, computers and stock is more than likely to have a minimum security condition.
This is simply a list of requirements that insurers insist on there being in force to protect your business in the event of a loss, through theft. This is irrespective of the value of contents and stock that you need to insure. Usually the higher levels of stock that you have, the more onerous the requirements. This can be anything from roller shutters to a Redcare GSM intruder alarm.
There is a minimum level that they all need you to comply with though, in terms of locks for doors, roller shutters and windows.
For windows, these are usually split between accessible windows and non-accessible ones. Accessible windows are usually those you can reach without the need for ladders or scaffolding, but beware of windows next to low roofs, insurers treat these as accessible.
As far as door are concerned, insurers want there to be a minimum level of locks. You cannot rely on any old key operated lock, many just need a bit of pressure and you will find that the door opens. At the base level there are two types of locks. The traditional Yale lock, that you would use to open your home front door and a mortice lock, which is more substantial. Most business insurance policies will have a requirement for the second type of lock as a minimum.
With the ease of purchase over the internetfor most physical products nowadays, you need to make sure what you are buying (if it is a lock) is fit for purpose. Your policy will state that the lock needs to be at a certain level, this is British Standard 3621. There are many different BS levels, but most policies will have a requirement somewhere in the wording, that your door locks have to be BS3621. In addition, there may be requirements on the thickness of the door jambs and the striking plate (where the locking bolt actually fits into) distance from the top and sides of the door frame.
You are always better getting an approved locksmith in to do the work for you, however if you want to do it yourselff, please make sure you consult the relevant part fo the policy wording.