Neither HMRC nor Companies House will definitively state that they waive their late filing penalties when you strike off a company. However, it is common knowledge that if you have Companies House filing penalties and you choose to dissolve or strike off your company, they will allow the Strike Off and the penalties will be forgotten.
From HMRC's perspective, they will commonly block a strike off application if the company has outstanding returns to be filed, yet they will usually allow the strike off when there are minor unpaid late filing penalties and no tax due. We will not provide you with blanket confirmation that these fines will not be pursued, but it is common that they will die with the company after 6 years.
If you subsequently choose to restore the company, it is very likely these penalties will reappear.
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