Russian invasion of Ukraine

The moment one launches the US and Britain would retaliate right? You can't just let off a cheeky nuke

Depends who it's aimed at, but largely, yes.

Depends 1980s Staff College war games saw Birmingham nuked followed by us hitting Kyiv(ironically) then stopping ( targets were chosen to be big but not too emotional).

With the nukes you'd have to hope there's a chain of people between Putin and an actual launch

https://youtu.be/F7qOV8xonfY

You can't just let off a cheeky nuke, it's full blown irreversible destruction the moment a launch is detected

If that had been that case, it would probably all have ended in 1983: https://en.wikipedia.org/wiki/1983_Soviet_nuclear_false_alarm_incident

On 26 September 1983, the nuclear early-warning radar of the Soviet Union reported the launch of one intercontinental ballistic missile with four more missiles behind it, from bases in the United States. These missile attack warnings were suspected to be false alarms by Stanislav Petrov, an officer of the Soviet Air Defence Forces on duty at the command center of the early-warning system. He decided to wait for corroborating evidence—of which none arrived—rather than immediately relaying the warning up the chain-of-command. This decision is seen as having prevented a retaliatory nuclear attack against the United States and its NATO allies, which would likely have resulted in an escalation to a full-scale nuclear war. Investigation of the satellite warning system later determined that the system had indeed malfunctioned.