Ignoring all the populist nonsense in the OP, the way in which the country will pay for this has already been mentioned. We will pay slightly higher taxes than would otherwise have been the case.
The Government is going to borrow the money required, which will be at very low rates of interest. Collectively, we will need to service those debt payments on an annual basis. If we can return to something like normal levels of economic activity and growth (which is the entire point of these interventions) then we will hardly notice that at all.
Also, once inflation has worked its impact, in 30 years’ time when we’re finally paying this off, the amount borrowed won’t even sound that high. A bit like when you first buy a house and the mortgage seems enormous but, by the time you come to pay it off, young people can’t believe you were able to buy a house for that amount.