I've commented below but "due to the nature of your business" can be because its a newly formed company with few employees and no trading history trying to deposit £700K getting to many points on the banks "is this possibly a terrorist/money laundering/drug dealer" system and getting overzealously denied.

It's currently far more damaging to a bank to give someone an account to perform illegal activities than it is to deny one to a legitimate company. And accounts that are in the gray zone (where transactions keep getting flagged and have to be checked by compliance) are likely to cost far more than they make the bank.