SWR should have been compelled to renegotiate the lease on the 707s beyond the point they'll now be disposed of, retaining the existing fleets and avoiding the appalling waste of 458s fresh from hugely expensive rebuilds being binned. Similarly wasteful disposing of the retractioned 455s.
150s are unavoidably ancient, although presumably DDA modified examples will be expected to do another ten years or so. The next SE franchise going for new trains quite simply shouldn't be allowed to happen if we are awash with surplus rolling stock. Overhaul and refurbishment are available, make do with it. From dire shortages to wasteful excess; the industry needs to get a grip. Apparently there's a shortage of cash and the railway needs to be frugal. You wouldn't think so. Perhaps the government needs to think outside of the box here. Create a state owned ROSCO and reacquire this surplus stock that used to belong to the country. Overhaul it and offer it to TOCs at a sensible price, thus reducing overheads and subsidy. Yes ultimately that's still public money subsidising something, but better it subsidises state assets than subsidising train manufacturers through massive leasing costs.
The whole point of allowing private finance in was to cover large investments in rolling stock that the state was not willing to meet. There are mismatch issues with the Networkers and modern traffic requirements. SW chose to replace the fleet for sound reasons as they saw it; why should SE not be able to do the same? Frankly weve seen what happens when the DfT starts intervening in such decisions with the whole new Gatwick fleet wasted then replaced with unsuitable trains that should have been retired, then replaced again, not to mention the imposition of 313s on the south coast.