You can change accountants any time but it may be wise to plan the move beforehand. Check all your deadlines including statutory deadlines like VAT returns, annual accounts, tax returns etc and see where you are in terms of preparing them. If your current accountant is in the middle of working on something for you, it may not be a good idea to move the task to a new accountant. It may be better to finish it with your current accountant and then change accountants. However, you should definitely start talking to a new accountant earlier, so you can plan the dates together to ensure smooth transition.