" have tried to get as much information from my dad but he is now 92 and partially death" - assume you mean "partially deaf". If so I do not see why this would be an insurmountable problem.
If as you say your name being on the bonds was unknown to you and non of the benefit came to you this should be easily resolved by your father writing an appropriate letter to HMRC advising that the whole capital and income was his personal income (and sole assets - having been wholly contributed by himself) and when and where he disclosed this income for taxation to HMRC. If he is liable to tax then clearly he would need to ensure that he declared the income for taxation at the appropriate time or take advice from a suitably qualified tax adviser to deal with any necessary disclosure. If he could do that it should get you out of that particular hole.
I am not quite clear or convinced as to your statement that the income was taxable on the remittance basis as opposed to the arising basis - but of course this could be correct depending on your father's residence and/or domicile and years he has been in the UK.
You do however also need to address your own personal "SA dividends" as if you were resident in the UK and taxable on your worldwide income you might also have had to declare the income to the UK tax authorities - subject of course to double taxation relief and/or restrictions on monies that could not be remitted from SA.
Hope that this helps.
regards and hope this helps
Operates Nationally with competitive costs
and email and phone contact (mob 07751720507) can be obtained from websites