Every year almost all limited companies have to prepare two documents - a set of accounts prepared in line with the Companies Act, and a Corporation Tax return for HMRC showing how much corporation tax the company is proposing to pay and why. HMRC get a copy of the full accounts too. You can't treat preparing those two things as distinct jobs - the profit you work out in the accounts informs the tax calculation, and then the tax bill you work out via the tax return informs the accounts. It's two bits of the same job.
There's a third document that the vast majority of small limited companies prepare - abbreviated company accounts. A company has to make some accounts available for the public to see at Companies House. It's quite permissible to send in the full accounts, but it's also possible to send Companies House a cut-down version - abbreviated accounts.
Abbreviated is the key word there. Often, company owners attempting to fulfil the requirements of the law submit abbreviated accounts to Companies House online without giving much or any thought to the full accounts or the tax return. But the abbreviated accounts just can't be competently done first. They come last, after the actual accounts and tax return have been done.
Companies House really encourage this by making it temptingly easy to submit abbreviated accounts to them online. Effectively, bang numbers into a template and keep clicking check until you get a green light. Down the line, an accountant gets a call saying "I just need someone to do the corporation tax return, I've done the accounts" and the heart sinks. The corporation tax isn't a separate job, it's part of the whole. Maybe the abbreviated accounts weren't so wrong that you can't reverse engineer some full accounts that aren't perfect but are acceptably consistent with both the abbreviated version and the truth, and a corporation tax return as well. But very often that isn't the case - especially if the business is halfway profitable, the fact that the tax bill hasn't been calculated and incorporated means that the abbreviated accounts are doomed to be misleading from the outset.
We don't really blame business owners for this, by the way - it's really driven by Companies House and HMRC trying to produce templates that make it easy for non-specialists to submit something to them. But - some things are specialist, among them the UK taxation and accounting systems!
So, if you're in that position, bear in mind that to prepare abbreviated accounts you must have something that you're abbreviating!