Vera

The boot well is the one people never lift, and it holds water for months without any smell.

On drying it out, because half measures do not work - I chased this for a whole winter before finding a blocked drain.

Lift the mats out entirely and dry them somewhere warm. Then press a hand into the carpet underneath, especially the front passenger footwell, which is where leaks collect.

If it is wet, find the source before drying. Common causes: leaves blocking the drainage channels at the base of the windscreen, a blocked sunroof drain, a perished door seal, and a badly fitted windscreen. Pour a little water in the relevant channel and watch where it goes.

Dry it properly, which takes days. A dehumidifier in the car with the doors shut for a few hours is dramatic if you can run an extension lead. Otherwise a fan heater on a dry day with the windows open, repeated.

Then keep something absorbent in the car over winter. Moisture absorbing bags for cars are cheap and they genuinely help once the source is fixed. They are useless while the carpet is still soaked.

And check the boot as well as the cabin, a leaking rear light seal or a wet spare wheel well produces the same symptom and is the one nobody looks at.