The short answer is no, you do not have to be an accountant to submit accounts to Companies House. However, it is would be best to employ services of an accountant. He/she would ensure all the changing regulations are complied with. Further, the accountant will be able to identify any tax savings. These tax savings may outweigh their fees.
It would be best to employ a Chartered Accountant for this. There are many people calling themselves accountants. However, they have not undertaken any professional examinations and are not monitored by any one. Chartered Accountants are monitored by their Accounting body. They are required to keep up to date with changing regulations.
Before employing an Accountant please check that they are a qualified Chartered Accountant.