Richard
I would say that depends on the work you are doing. Domestic only, £1m would be enough. If you work for a council they will want £5m. Most people these days start with £1m and increase as necessary. We get people saying they have to have £5m to be able to tender for work. We can issue a letter to say you currently have £1m but if you get are successful with a tender and win a contract we can increase to £5m. This seems to work and therefore you are not paying for something you may never need.
Feel free to contact us if you need any advice.