A lot of businesses will go bust, meaning that there will be high unemployment. Fewer people paying taxes and more people claiming benefits will put a massive strain on a financial system that will already be struggling to repay the massive government expenditure incurred during the lockdown.
Further, fewer people in work will mean fewer customers for the leisure sector (such as bars, restaurants, etc) and for stores selling non-essential goods. That, in turn, could lead to yet more businesses going bust and more jobs being lost.
We've still not fully recovered from the 2008 financial crisis and what we've got to come will be many, many times worse than that. So we're in for at least a decade or two of fairly high unemployment and tight financial stringencies.
However the UK Government's strategies for trying to keep businesses afloat and to save jobs will probably leave the UK in a far better position than in those countries where people have simply been left without jobs and where businesses have been allowed to go bust. In particular, the USA faces the prospect of a return to the 1930s for its economy unless their lockdown period turns out to be far shorter than many experts think it might have to be.