Vauxhall Zafira cutting out when disengaging clutch?

I have a T registered vauxhall zafira 1.8 petrol that had recently developed a problem of cutting out when I am coming up to junctions. It starts and idles fine but when I declutch as I approach a junction the revs drop right down to below 5000 and sometimes the engine cuts out. It has been serviced and new spark plugs fitted. Any suggested solutions please.