I know, sounds daft but it did. Could it be the heat exchangers are on the way out? They are about 5 years old now and of uncertain origin. The only reason i'm asking is (apart from the smell) is because i've been getting bad headaches and tiredness of late and am wondering if i'm being slowly poisened. But cabbages? seriously?
The HE exhaust pipe bits are normally quite robust, but you might have a leak elsewhere getting sucked into the fan. Worth checking, CO meter if you've got one. I once hired an Escort van with ropey rear door seals and got a good dose of CO. It's not pleasant at all.
Think i'll visit B & Q tomorrow then. I need to instigate an expedition underneath anyway because my solenoid is also sticking intermittently. In for penny etc etc cheers guys
Have you just used your washers? water can get stagnant in the washer tank, take the filler cap off and give it a sniff. You can now be a washer and a vent sniffer! I would drive with the windows open until problem found.
Rotting animal glues .. Damp mats ? A cabbage stowed with the kit under the seat ? Brake fluid leaking?