I think it used to be that a government losing a vote on a budget would mean a general election but since the Fixed-term Parliaments Act 2011 I believe there has to be an explicit vote of no confidence in the government (or a two thirds vote by MPs) to trigger an election.

https://en.wikipedia.org/wiki/Fixed-term_Parliaments_Act_201...

Of course, somewhat inevitably, since that Act was introduced I don't think any government has actually had a full fixed term...