It would be best to have a quiet word with someone who knows.
Overdrafts are unsuitable for long term finance as they are repayable on demand. The fact that a bank has given the facility is a sign that the bank at least has faith in the company. I do not know what business the company is involved in but if they are, for example, importing and distributing then a large order would be needed to get the best rate with the supplier so a £100k order might be placed twice a year to generate £300k in sales and an overdraft would be a good way to finance this.