Another coolant issue..

[Themoog]

Not long ago I had the thermostat replaced in my M62tu and last week I also had to pull off the main coolant hose going from the top of the water pump.
Today I was going to to put in a new timing chain tensioner so I removed the air box etc an noticed coolant all over the front of the engine.
The header tank was also empty.
I cleaned everything down, dried it all, topped up the coolant and have had it running for 30 min to pressurise the system.
As yet I cannot spot any leaks anywhere.
I thought it might be the seal on the water pump failed but it's dry.
Any ideas chaps?
I did notice that when I switched the motor off I could hear either air being pushed out of the filler cap but it's dry around that too.
Stumped. UK... 🤔