I wrote on this yesterday.

Lord Lawson, the former Chancellor, has rejected Ed Miliband’s proposed limit on the UK market share of banks:

"I think there are a lot of problems in banking, which we identified in the Commission reports, but I don’t think a lack of competition is the main problem"

Mark Carney, governor of the Bank  of England commented:

“Just breaking up an institution doesn’t necessarily create a more intensive competitive structure.”

John Cridland CBI Director General had this to say:

"an 'arbitrary cap' on market share was not the way to boost choice in banking."

If Mr Miliband wants to improve competition and value for money for the UK public, then that is a worthy aspiration.

He may though be better advised to engage with the banking industry in a dialogue designed to address his concerns, as opposed to proposing market intervention that will have potentially distorting and harmful consequences.