It is normally the Official Receiver or the Trustee in Bankruptcy that would be responsible for putting the charge on, not Inland Revenue.
I think you will find that, once the charge has been placed, they (under the old law) had an indefinite period to take action to ask for the money or to sell the house. There was no obligation on them to do so at any particular stage. Almost certainly, they have the right to add interest throughout the period.
I assume they have now corrected their error and placed the charge. If they haven't, I think they only have until 31.3.07 to do so and take action.
Your father should get urgent professional advice (probably from an Insolvency Practitioner) to see whether there are any steps he can take to reduce or remove his liability in view of the very long time this has been going on.