Some good advises in here
I would use a strong all purpose cleaner (APC) mate. Rub it on with a microfibre cloth. Wouldn't waste your time with Tardis, as it's a solvent based tar remover.. not sure why you'd use that inside a car..
traffic film remover (TFR) is also pretty strong alkaline based stuff, so if the APC isn't working, you could try some of that. I would try the APC first though, at various strengths starting at maybe just the usual 10:1 all the way down to neat! Only if this fails, step it up to the TFR, and make sure once the stains have gone, that you then wipe clean with fresh water on a cloth. Don't want any chemicals sticking to your skin next time you put your arm on the rest!