Accountants belong to professional organisations that make sure their members abide by certain codes of conduct and work in a competent manner. Sometimes, however, problems may arise.
If you aren't happy with the service your accountant is providing, you should first explain your complaint to them. Be sure to set out how you'd like your complaint to be resolved. You should also check if your accountant has a complaints policy or process.
If the accountant doesn't provide a good enough response, put the complaint in writing and send it to the person named on the complaints policy, if there is one, or the senior partner (or principal if the firm is a sole practice). You should say what you'd like the firm to do and set a deadline by which they should put things right.
If you're still unhappy with the actions of the accountant, you should complain directly to their regulatory body. There are professional bodies that regulate the accountancy profession, but for most consumer-based accountancy work, the regulatory body will probably be one of the institutes of chartered accountants.
There are institutes for each region of the UK:
England and Wales
You can complain to these regulatory bodies by filling out a complaint form on their website or by complaining in writing.
Going to court should be the last resort if you think the professional bodies haven't dealt with your complaint properly. An action against an accountant is likely to be for a breach of contract. If the sums involved are substantial, you should consider using a solicitor.