Companies that operate without professional indemnity insurance are in breach of regulation and run the risk of fines, not to mention the costs associated with a claim. Your firm could very quickly be closed if you are not able to secure PII.
In order to find the right insurance for your firm, you need to ascertain exactly how much cover you actually need. Your income and turnover will influence this considerably. In general, firms with a turnover exceeding £200,000 should look for a £1million limit of indemnity, whereas those with less than £100,000 turnover may only require around £250,000.