Australia is a bit more fortunate than the poms in this regard.
In England, they only need one clown at the top, the PM, to decide that the GST needs to go up and then that is the new law. He can make it as high as he likes.
The new 20% GST rate that they haver just bought in is an obscene rate to pay on top of income tax.
I can see it being an anchor to drag on the whole british economy.

In Australia, to change the GST requires the approval of all states, and agreement from all states about anything at all has been traditionally very hard to get.

Unfortunately however, it is still possible if they are bribed with the prospect of getting more money, which a rise in the GST rate would provide.

I hope they would not be swayed by this as the extra money from the GST would only be a temporary thing.
Already the present government is trying to take back 30% of the GST to finance the hospitals. Once they do this it means that the original sales pitch that 100% of the money raised by the GST would be given to the states for state projects would be proven to be a lie.
Fortunately, in W.A. Col has resisted this money grab resulting in some considerable annoyance to the federal government.
Good on ya Col! Stick it to 'em.
The other states seem to have folder.
So their 100% of the GST payments is now 70%.
Weak and useless twits!

It wouldn't matter how high the GST rate went. In the end, the federal government will try to take control of as much of it as they can.