That depends on whether there's interest to pay. Assuming there isn't, it would be One pound, twelve and a half pence. I'm sure it wouldn't hurt you to round it up to �1.13. (One old shilling became five new pence in 1971).
In absolute terms Jenstar is correct. However you are right in saying that this is not what it is worth. Even without considering interest or the time value of money, the meteoric rise of wages means that a pound today is worth a fraction of a pound in 1968. There is no correct answer to this, and the repayment should be negotiated between you and the people you owe.