That depends upon interest rates. But once debt to GDP goes above 90% you are very vulnerable to interest rate changes if you are running a deficit and have maturing bonds to raise funds for, to replace. Your future is in the hands of the markets and market sentiment.
The plus for the UK is that our bond maturities are longer than most countries with an average of 13 years, the bad news is that after Ireland we are joint second with Japan as the most most indebted country on Earth with public, private, industry and off balance sheet debts like PFI at about 500% of GDP. Once you add in public sector pension and retirement pensions then it gets really ugly at about 900% of GDP. Quite obviously neither is affordable, which is why they will hyper-inflate them away or default on our obligations / debts.
http://www.moneyweek.com/endofbritainGreece, Portugal, Spain and Italy have shown how quickly markets will punish a country, once confidence is lost. We have only got away with it so far because we have our own currency and the Eurozone countries we going to be in trouble first. Our time is coming with our AAA rating lost this year and if we have another year of no growth (likely) and missed deficit reduction in next Novembers budget statement, so the balanced budget can is kicked another 12 months down the road (likely), then the wheels are going to quickly start falling off the UK economy, unless the markets are still focused on the Eurozone where things have gone from bad to worse (still very possible).
Countries like large businesses normally take longer than expected to go broke, where there is much maneuvering to stave off the inevitable. Greece, Portugal, Spain and Italy are all examples of this with the jury still out of Ireland.