So, in case anyone else is interested...

I called Panasonic and kept getting told that I should send the camera to a
service centre. Probably cost loadsamoney and be cheaper to buy a new
camera.

But eventually got put through to talk with an engineer who was massively
helpful and talked me through it.

1. Use a hairdryer to warm the black ring that surrounds the front of the
lens, the ring with "Leica" written on it.

2. When it is warm gently prise the black ring out. It is held on with
double-sided sticky tape.

3. Remove the four small cross headed screws.

4. Look for the next 3 screws and remove them too.

5. Gently pull front lens off.

6. Clean lens with airbrush

7. Reassemble.

Official Cautions: Take your time. Don't touch lenses with fingers. Take
your time. Do it gently. Take your time.

And look, I post this here in case it helps someone else. If you do this to
your camera and bugger it up then don't blame me.

Bill