My idea:
The Government actually make a decision for once and allow LHR, LTN, LGW & STN to build 1 extra runway each. Forget noise issues and planning issues, forget only building a possible extra 1 runway at LHR or LGW or building a Thames Airport then closing LHR because whatever decision they make now is only going to be ready in 15-20 years time.
There probably isn't a huge need for 4 extra runways but there will be in years to come and if it's going to take another 15-20 years to build 1 runway we might as well put the work in now so we don't have a similar situation in years to come.
We don't need new airports, we just need the existing ones to develop further to help our economic growth. The longer it takes for our Government to finally make a decision the further we get left behind.