Our business uses Xero accounting and about to set up another business with an investor. As the financial reports will be different is there a way around having to set up another Xero account, could we just use the one?
Short answer (from my point of view) is no.
Each file has its own ABN, specific to the entity running the business.
Running reports for two businesses from one file is a nightmare, you will struggle to get relevant information on a timely basis (the key purpose of such systems). While you can (with manipulation) get the report format set up OK, you will still have a jumble of numbers and a lack of clarity.
Assuming your investor wants to know what is happening with the new business, do you want them having access to your existing business details?
Some starting reasons to consider.