One interesting decision that Ed Miliband made this week was to appoint Karen Buck as his PPS, following the long-planned departure of John Denham. Tory MPs have told me they were very quickly given ‘lines to take’ on how this represented a big ‘lurch to the left’ on the Labour leader’s part.

CCHQ is right that Karen Buck is on the left of her party: as a shadow welfare minister she pushed for the party to oppose the £26,000 benefit cap when Liam Byrne’s official line was to leave it be (one he later reversed). But the line to take conveniently forgets that one of the principal purposes of a PPS is to act as a conduit between a leader or minister and the opposite side of the party. So a minister on the right of their party should in theory appoint a PPS on the left.

Now it doesn’t always work out that way: Owen Paterson, for instance, seems to be pretty good at appointing PPSs who occupy the same ground that he does in the Conservative spectrum (and indeed PPSs who like resigning, or at least threatening to). But Buck might well be a useful conduit between Miliband and the left of his party on issues such as welfare when the thermometer is rising on this policy issue. She has established herself as an expert on this area in parliament to the extent that even her greatest critics on other parts of the political spectrum praise her knowledge and passion for the subject, while insisting that she’s totally wrong.

This could well come in handy for Miliband, but party sources insist to me that she was picked not because she’d be strategically useful on specific policy areas, but because she is popular and well-respected in the party and works hard on campaigning. Indeed, she became something of a celebrity in the party in 2010 for beating Joanne Cash in her Westminster North constituency: I saw young party activists approaching her to sign their conference agendas at that year’s Labour conference, so great was their admiration.

That as may be, but it’s worth watching how the leader deploys Buck when the welfare debates in his party start up again.

Tags: Ed Miliband, Karen Buck, Labour, UK politics