Theresa May was wrong. There is a magic money tree. The government can create money just by adding a few zeros on a computer.
What there is not is a magic wealth tree. Money is just a convenient representation of wealth that allows us to account for wealth and move it around easily.
We can't make ourselves wealthy by printing money. Every time we print we are effectively taxing the currency. All holders of the currency pay this ultimate stealth tax every time we print.
Unfortunately the markets have decided we can no longer print money without consequence. If we do the exchange rate will go (further) down and cost of government borrowing up. The amount that the markets will allow the government to borrow has also reached its limit. Debt is no longer cheap or without consequence, as most mortgage holders will tell you.
Some things government(s) could do :
i) Spend less.
ii) Keep spending the same and keep taxes the same.
iii) Fund any spending increases we want to do through taxes.
iv) Get better value for money from the money we do spend.
v) Keep spending the same but shuffle it around between different areas.
vi) Grow the economy so we have more money to spend.
What the government(s) can't do :
Keeping spending more and taxing people less.
When the money markets called time on our spending, it basically scared the crap out of the government. So there will probably be some overcompensation over the next couple of years in what the government(s) will choose to do.
TLDR, we've reached our credit limit.