'More operations needed at Heathrow' is a bit like the 'red car effect' (you know - manufacturers make red cars because people buy them, people buy red cars because that's what the manufacturers make!)
There is an assumption that the London/Essex SE England area must have all the runways, because that's where people wish to travel from. But is that really the case? For example, why do airports such as Bristol have such appalling road/rail links? Why have all the ex-USAFE aerodromes in East Anglia been allowed to deteriorate?
What is needed FIRST is investment and expansion of existing airports away from London, Gatwick, Stansted, Luton, Manchesterr BEFORE anyone starts trying to build green field airports. However, personally I think that Alconbury would be a reasonable site for a future airport. But would the interests of Conington, Sibson etc be protected? The only other real choice would be Foulness.....