there is serious opposition to increased air traffic due to environmental issues. Filtering people onto larger aircraft rather than having numerous smaller aircraft flying direct from the regionals is one answer to this.
This idea has been promoted by the green lobby. If you're contemplating allying yourself with the eco-extremist agenda in the hope of crushing regional long-haul services in favour of LHR dominance then you'd better be careful what you wish for. Firstly, the eco-extremist lobby does not desire an expanded / dominant LHR; they want it reduced and capped.
Secondly, you need to take a closer look at those regional long-haul services. Have you checked up on them lately? Where are all these "smaller aircraft" you speak of? At MAN, around 32 long-haul departures will operate each day in Summer 2016. Only two of these are scheduled as narrow-body types [2 x UAL B752] - and they fly pretty full. All the other flights are programmed as widebodies and historic load factors are strong. Services are only sustainable at airports like MAN if they are profitable. No airline feels the need to be seen flying the flag there. I don't have the full long-haul schedules to hand for BHX, NCL, GLA and EDI but the same principle applies.
Now, consider the situation if the eco-extremist lobby were to succeed in getting long-haul flights from the UK capped. Do you think LHR would get the full quota? Well, think again. London and the SE has roughly one-third of the population; the rest of the UK has two-thirds. But L&SE has the vast majority of long-haul departures already. Are politicians outside London going to stand meekly by as regional airports are stripped of their relatively meagre share of economically vital long-haul links in favour of more concentrated LHR dominance? Or might LHR instead be forced to trim its phenomenal frequency of multiple-hourly departures to New York, for example? Those regional long-hauls are not "smaller aircraft", they are large aircraft just like those at LHR and their load factors are strong. All hypothetical at this point, but never assume that LHR will get all the cake if a cap on flights were to be introduced.
As I said, be very careful what you wish for.
You also have the chicken and egg situation whereby businesses may not want to invest in areas that do not have easy access
Quite so. Another reason why regional political interests will not allow themselves to be asset-stripped of their portfolio of essential long-haul schedules in favour of even greater concentration at LHR.