Did you see that the Carillion pension fund is made up of quite a few sections? Just one very small part is actually in surplus... the Directors' section!
I don't agree. If the nationalised company is big enough to have internal (i.e. not-for-profit) departments it means that an enormous amount of money stays within the company instead of funding all the overheads of the services bought in, like interest on the working capital, Professional Indemnity Insurance, Directors remuneration, dividends, etc etc.
If the great advantage of nationalisation is that we can scrap comparatively minor things like indemnity insurance and directors' remuneration then, being charitable and assuming we can reduce those figures in the case of Thames Water by £5m, we would see each of Thames Water's 15m customers save just 30p on their annual bill.
If the advantage of nationalisation is that we can lower revenue on the basis that shareholders are not expecting a dividend (or interest on working capital) then, as I say above, that's fine but that means that McDonnell mustn't double-count and on the one hand say that we need to dispense with these evil profit-hungry companies whilst on the other hand saying that continued profits will cover the acquisition cost.
There are only two ways in which this could work.
Firstly, we could under-compensate shareholders / creditors against the market value (which, to be fair to him, McDonnell has hinted at). I am sure you can appreciate how catastrophic this would be to future investment in the UK, however.
Alternatively, we could change the pricing structure of the industry and make it more like taxation, so richer customers paid more per litre (or kilowatt-hour) than poorer customers. Perhaps this is a vote winner for Labour, but it should be announced honestly if it is indeed the plan.