I have Zafira C Tourer and when limp mode occurred the first was to replace EGR valve, then also replacement of intercooler hose, but for this knocking sound I would think of the valve. Check if the exhaust smoke smells or look differently.

 

thanks for the reply, at the point of it going into limp mode then making this noise there was no smoke or bad smells and the oil colour and level level was fine

 

I'm just saying what happened in my vehicle. Reading further into causes of limp mode that can be anything, as the limp mode is just a engine's self protection from further damage. This needs to be checked in the garage.