Help! Brake lights stuck on!

[Odd Job]

Morning all,

Can anyone suggest where I start looking to try and sort this out please?

This morning when I went to leave for work it was very damp.
I fired the car up, went around all the windows with my squeegee to remove the moisture, got to the back of the car and my brake lights were on.

Ok, damp is probably the key word here.

So, switched the car off. Then back on. Brake lights still on.
Turned all the lights on, checked. Still on.
Turned everything off. Still on.
Moved the car. Still on
Let the car warm up with the heater on. Still on.

I work roughly 20 miles away from home.
I need to get to work, no quick option, so very bad of me, I drove into work.

I get to work, reverse the car up to the office window, I can see the reflection of my brake lights. Everything is working fine.

I have no idea when they decided to work correctly, or have any idea where to start. I'm thinking damp weather.
Obviously damp weather will only continue to increase this time of year.
If anyone has any ideas where I can start to look to identify the problem that would be great.

The car is a 2005 ZT 2.0 cdti manual. No cruise control, no traction control. A fairly basic spec.
Many thanks in advance.

Richard