Vauxhall Meriva when key is turned nothing but a clicking noise. battery fully charged.

Could check battery terminals and wiring at starter . But does sound like a flat battery . A lot can happen in 6 months with a battery and you need to check the voltage to eliminate or otherwise before getting too involved .

Definitely not a flat battery as I removed battery to put it on charge but it was fully charged anyway. The terminals were spotless from being cleaned when the battery was replaced.