I have realised I have blackbirds nesting in a tree/bush in my garden. There's a magpie keeps trying to get in and the poor blackbirds are having to fight it off. Is there anything cando?

1. The answer is no. That is Nature. Theses events happen  every year at many nests. If a Kestrel or anny other raptor attacked a nest. Most birds of prey/raptors are schedule 1 protected birds, not all raptors. But the general answer is no.

Thanks, I just wanted to check there was nothing I needed to do, thank you for your help. 

Yet again, a magpie has predated the blackbird nest here. They fail every year. Saw the magpie with an almost fledged youngster and both adult blackbirds within 6ft of it alarm calling……to no avail.

Yeah that's my fear, 

Sorry you are witnessing this,  I understand how upsetting it can be seeing attempted and successful predation;   I also saw a mature blackbird fledgling taken by a magpie up on to a nearby roof with the blackbird adults alarm calling but sadly it happens in nature and it's hard to watch.    Blackbirds will likely have two broods or even a third and will hopefully find a safer nesting place next time.