A judgment attracts interest from the date of the judgment (not the date of registration of the judgment mortgage) at Court rate (about 8% iirc).
the judgment mortgage secures the debt against the property - i.e. anyone buying it buys it subject to the debt, so if your friend is thinking of selling, it will have to be either paid off, or an arrangement that the debt will be paid out of the proceeds of the sale will have to be made.
If your friend doesn't attempt to pay off the debt, in theory the creditor can apply to court for a well charging order, which gives them a power of sale over the property, and ultimately they can apply for an order for possession and order for sale.
In short, it's not too late to start paying off, but for the reasons above, it would be a very good idea to start paying it off.
The other option is to bury the head for 12 years and hope that the creditor forgets about the debt and the Statute of Limitations period runs, and then apply to get it cancelled on the basis it's statute barred, but that is obviously a very risky strategy.