I suggest that you talk to an accountant. Any accountant in your market should give you a free initial consultation. Then you can decide.
In principle you do not need an accountant. Just as I do not need a gardener. It is largely a personal choice based on how much you value your own time that would have to be spent doing it yourself, and on how confident you feel that you could do it and get it right without assistance.
Check the accountant's qualifications and whether he is regulated and has insurance. Anyone can call themselves an accountant.
Aside from the fact that he saves you the time of doing it yourself, he should also (generally) get to a more accurate profit figure. Overstate the profit and you pay too much tax. Understate it and you run the risk of penalties. He should be able to identify deductions that you might not appreciate or might be nervous about claiming. If he gets it wrong then you may have some redress.
There may be more assistance that he can provide over and above the mere completion of accounts and tax returns.
The charge will normally be a function of the amount of time that the accountant spends and the extent to which he can delegate work internally to lower-charge-rate staff depending on the complexity of the work involved. Depending on the accountant he may offer a fixed fee, but it will have caveats concerning the standard of record keeping.
Anyway, as an accountant myself you may consider me biased.
For someone like you I would expect our firm to charge about £250 per year plus VAT. Don't forget the VAT (20%). It comes as a rude shock if they quote you a net figure and you are not VAT registered and cannot reclaim it.