The UK used to have a Landing Card system for all non-EU/EEA/Swiss citizens. You had to fill it out on the plane and present it at passport control. It asked basic questions but did not ask anything about criminal convictions.
The Landing Card system was abolished in 2019, with Britain trying to appear more open to the wider world as it turns it back on Europe.
Also, Heathrow and a number of other larger airports now have an e-gate system where you can scan your passport and, if there are no problems, go straight through and enter the UK without seeing a border officer. The e-gates used to be only available to UK and EU nationals, but at Heathrow they have expanded it to other "trustworthy" nationalities, including Australians: https://www.heathrow.com/arrivals/immigration-and-passports
So you could in theory arrive at Heathrow and enter the UK legally without going through a human official.
As AB2014 says above, even if you went to a human passport officer, it's extremely unlikely that they routinely ask all travellers if they have a criminal record. I have been to several non-European countries and gone through standard immigration checks, with a few basic questions about why I'm there, where I'm staying, how long I'm staying, etc., and I have never been asked about criminal records.