@neil I would hope so, gas explosions are no fun. Here in Germany they come with sirens and stuff. We had a leak a few years back just before the coldest weekend of that winter and yeah, no heating that weekend. I think it was 2021-2022.
I hope, it's just smelling from somewhere else and doesn't come back.

@neil if this was a garage full of oil the US would be there.

@neil Yeah, people complain that "nothing works any more" in the UK, but one thing that does still seem to work, in my experience as well as yours, is the speed of response to a report of a gas leak. On a good day it's minutes rather than tens of minutes.

@neil what do they do in this instance? Cap the supply until you get an engineer to fully investigate or are they happy to leave you connected?

Our CO alarm went off a few years back and they capped us until we could get a gas safe engineer out to investigate (again finding nothing). Those were 3 days of some freezing temps in the house.

@neil Is there anything in your garage that could have leaked? Camping stove, weird solvent that's evaporated etc.?

I once had a weird smell outside for days, couldn't find the source, this was more solvent than gas admittedly. It eventually went. Weeks later I found an empty split bottle of white spirit deep in the garage, liquid evaporated. The smell had carried in a really odd direction.

@neil pipework rather than boiler, I guess.

Or weird smelling soil. The gas board dug up our road in London countless times, because there was an area that often smelt of gas but they never found anything - in the end I think they put it down to funny smelling dirt.

@neil Eek. Where does your supply pipe run before it hits the meter? Could the leak be upstream of the point the engineer isolated your boiler?

I'm sure you've already thought of this but it's where my mind went..

@neil any way it could have leaked in from a neighbouring property?