While both are true, interest rates are at all time historic lows, now is the best time to "borrow" in a century, "borrowing" now could save Bns in interest on future borrowing. Of course in the UK none of it is actually borrowing because the govt controls the Bank of England that issues the currency, so the govt. is actually just "borrowing" from another element of itself, the bonds are readily bought up at the moment because spending now would so obviously deliver benefits to the recovery. The BoE is currently quantitative easing ("printing") hundreds of Billions of new money into supply with no impact on inflation because it's all going straight into increasing productivity or consumer spending. The idea that we should be cutting back on critical infrastructure spending because of an economic "finite finances" fallacy created by the British media elite will hamstring any recovery and ensure it's as flawed as Britains shockingly slow recovery from the 2008 economic crisis.
This is the first steps to austerity, a tried and failed approach economically that exists primarily now as a political tool to underfund services to then justify privatisation, inevitably ending with MPs selling off assets to their family and mates in underhand deals, just as Matt Hancock did recently amongst his many colleagues who have done similar during this pandemic.