Another interesting difference between the US and UK. Republicans do this routinely in the US, and have done for many decades now.
The last Republican president who didn't do this was George Bush (the first one). After promising "no new taxes" during his campaign, he later agreed to do the fiscally responsible thing and raise taxes in order to offset spending increases. He was not re-elected. That was ~30 years ago, and to my knowledge no subsequent Republican president has made that mistake.