Usually you will have to. However, a couple of things may help. First of all, if you can prove that there was a reasonable excuse for it being late, it may be possible to have the fine waived. This is not easy to prove though.
More importantly, the fine cannot exceed the amount you owe. So, if you are due a tax refund, regardless of when your return is in, you will not have to pay the fine. If you owe, say, £45, that is the most you can be fined.
If you cannot get your return in on time, making a payment of tax over that which you think you owe can mean the fine is not charged.
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