I'm very near to MAN thus not so concerned with those airports.
This seems to be the mindset of many R3 opponents.
To try and sum up a bit, the arguments for expansion at Heathrow or Gatwick come down to whether the hub requirement will be met or not. You will not turn Gatwick into a hub that could rival the plans for LHR without spending significantly more money than is being proposed at the moment. The LGW option is to add a new runway that will help Gatwick but do nothing for congestion at LHR. The debate on expansion there will still go on.
R3 will allow people from LBA etc. to take the shuttle down to LHR and fly to pretty much anywhere. There will inevitably be a loss of future new routes at Manchester that would not be viable without the pax from the other regions making the long drive instead of taking the shuttle down to LHR.
I would however say that those people deserve to make their own decisions and would rather take a cheaper taxi from home to the local airport and a 45 minute shuttle to an airport which will open up the world to them, also the chance to fly in large economical comfortable aircraft. (Before making the obvious comments about transfer times at LHR we are talking about building a new facility so that argument is invalid).
Now we have the cost of the project. The majority of this is coming from private investment and will boost our economy. The project will create jobs and opportunities throughout the whole of the UK as well as increased access to the rest of the world thereafter so this therefore is a win win situation.
The publicly funded part is the main cause for concern for some. This has been estimated at between 5 and 20 billion pounds. I cannot believe that figure has not been narrowed down and an actual budget been drawn up but lets just go with £10bn.
We now need to know the figure that would be required to maintain or upgrade the existing infrastructure had the expansion not taken place. The M25 and M4/A4 are in dire need of widening at this location anyway and this would not be cheap. I strongly suspect a large part of this cost is being shifted into the LHR budget but if R3 doesn't go ahead it will still need to be spent. We need to know this figure and minus it from the LHR budget.
This figure will now be significantly lower and I find it hard to believe that these sums have not already been done by somebody with the facts.
Now we will have the publicly funded part of the direct costs of R3. A large chunk of this cost will come back in taxes on wages and VAT so is not really being spent at all. There are not many civil engineering contractors based in Central London so this work would probably be carried out by companies from around the UK.
A figure can also be obtained of the proposed benefits to the country as a whole and this put side by side with the above. I do not have access to the facts to calculate the above and doubt anyone on here has but the calculation can and should be done.