MP's are being reminded to know where to draw the line in relation to Police investigations

David Seymour wrote to police in 2022, on behalf of Philip Polkinghorne, before he was charged with murder, then acquitted.

The Act leader's standing by his letter this week, saying he was passing on a constituent's concerns.

Police Minister Mark Mitchell says Seymour was acting in good faith as a local MP.

But he says it's a good reminder for MP's to be very conscious of boundaries - and not injecting themselves into an investigation.