I have not read wikipedia on NPV, but here is a linkUndercoverElephant wrote:No they aren't. They are in exactly the same situation.
https://en.wikipedia.org/wiki/Net_present_value
There is a massive difference depending upon payments schedules. If someone is given some money with zero interest payable over 1,000 years it is almost as good as a gift.
Adjusting the timing of payments and the interest rates means that the debt is payable off. It may not be paid off because governments decide to borrow more, but that is a separate issue. The UK has had sovereign debt for a long time (centuries), but that has not necessarily been a problem.