Thanks all for your responses.
I called Mercedes Roadside assistance out this morning and they came pretty quickly which was good. Apparently there is an issue with the transmission. Car has been recovered to my local dealer and I have C-Class estate as a replacement car which I dont like! But I shouldn't complain MB UK are pretty good like this, car taken to dealer and replacement car delivered home within a few hours.
I am bit upset that a transmission problem has occurred within less than a month of having the car. I feel like demanding a new car now!!