If you anticipate a problem in making a tax payment or meeting a deadline, it is normally best to try to communicate this with HMRC as soon as possible, although their resources will inevitably be stretched at the moment so it would be advisable to keep copies of any correspondence or notes of calls. Approaching the matter this way will assist in mitigating penalties down the line.
If you have received an automated penalty or assessment from HMRC then it is usually possible to lodge an appeal within 30 days.An appeal may be allowed where there is a “reasonable excuse” for the default, i.e. the omission arises where the taxpayer is not at fault or they are unable to comply due to circumstances beyond their control. The current Coronavirus situation is unprecedented and therefore may provide a solid ground for appeal in many cases. The key action is to lodge the appeal notice within the time limit with some narrative around the reason for default. Further details can be provided later if need be.