Car Take Back are mostly very good. There offers are usually pretty good (it seems to me they must use different scrap yards who I assume compete to offer their service to CTB) and they don't turn up and moan it's on steels instead of alloys etc.
I'd also suggest a cheeky 'Anyone buy scrap cars' message on local social media selling pages. It usually flushes out every man and his dog with offers from the hilarious to the good. Getting them to turn up is another matter, but you can bet your last quid someone will buy it. Would humbly suggest though if scrap pays (for example) £100 and you get offered £130 off some random bloke then take the scrap yard money as once it's gone, it's gone.
eBay could be worth a bash too, would suggest lobbing it up (with lots of pictures and good description) for about £250 and having that submit offer facility. You can set it to reject anything below 'X' value and accept anything above another price.
Those Mercedes are (I'm afraid to say) not known as one of the greatest cars of all time, but if the MOT costs little you might as well have it done then roll round in it for another year.