Wally wrote:
Hi, I'm a newbie to this growing lark, I've recently
taken a allotment and having a go for the first time this
year.
Been burying seeds and stuff and most seems to be growing,
however, looking at my broad beans today, they are
covered in black fly.

I wonder if you're new to this 'growing lark 'how you knew they were
blackfly? All aphids are harmful to plants. They can stunt them or
prevent flowers opening properly and distort the leaves. They also carry
viruses. Best thing is to take your thumb and forefinger and rub them up
and down the stem taking care not to damage the stem.