SHORTLY BEFORE his little spot of mortgage bother, erstwhile trade and industry secretary Peter Mandelson confirmed that the Post Office is to remain in public ownership - at least for the foreseeable future. He told the Commons that the necessary legislation for full or partial privatisation could not be introduced for several years: 'It would cause massive uncertainty, and diminish the chance of immediate reform now, which would be the worst outcome of all.' He emphasised, however, that the government did not rule out private shareholders at a later date. Mandelson also revealed that an independent regulator will be appointed to preside over 'careful and phased' dilution of the PO's monopoly. He will also consider management requests for 'further restructuring'. Meantime, there is jam today for the Post Office: the Treasury will in future be denied its current massive creaming of PO post-tax profits - averaging over 80% in recent years. The so-called external financing limit will drop next year to around 40%, from this year's £335m to £207m. The concession is intended to close the £1 billion pound investment gap faced by the PO over the next five years. The government will also remove the existing annual acquisitions limit of £20m and give the green light to investment plans.