Most countries hover around 100% of GDP or less in debt. Anything over that is pretty much considered bad. However, it really depends on why the debt increased. If it helps the economy more than the cost of interest than a lot of countries take such a huge amount of debt.
Also, it is harder than you think to repay debt. First, you have to pay interest. Second, funds are zero-sum. So if you use taxes to repay debt then you have to cut funding for something else. Considering the parliamentary system, the coalition may or may not have that much political capital to convince people that "hey, we really need to pay that debt rather than providing healthcare, for instance." People like to pass on the responsibility of repayig to the next generation. Just one of the few reasons why you see countires take more and more debt.
Hope that helps.