Hello and welcome to the site. Thank you for your question.
There are many people who run their businesses from home. You should not be unduly worried about it in the short run...as a start up business. If the business grows to an extent that your son is using the house for storage at a large scale (big lorries delivering and collecting books frequently on a daily basis, then maybe you should be concerned.
Some points to bear in mind...
If your son is using a room in the house as an office (home office) then don't go overboard with claiming high expenses for use of home as it may result it part of the property be deemed business requiring you to paying business rates and eventuallly CGT on part of the gain being deemed business.
Having said that, it should not be a problem in the short run .. review the situation as business grows.. he may decide to hire some business premises and the problem is gone.
I conduct my accountancy business from home... no problems.
I hope this is helpful and answers your question.
If you have any other questions, please ask me before you rate my service – I’ll be happy to respond.