KETTERING
SEN: 112 mi, 1 hr 59 mins
STN: 70.9 mi, 1 hr 15 mins
Note also that Cambridge and Peterborough serve Stansted with direct rail links and although some places like Stevenage, Luton,
Northampton etc. are closer to Luton Airport, they still come into the Stansted catchment area and a lot further to Southend.
I was really surprised and interested by your comments about Northamptonshire coming under the Stansted catchment area...
While it might be one of the airports target markets, I'd be extremely surprised how successful it is attracting people to the airport from this far away, unless you are one of the bargain travellers flying on a £10 Ryanair flight.
Getting to Stansted from Northants is fully reliant on the A14/M11 to get the airport. While in theory that means traveling on nice open dual carriage ways and motorways. The A14 is so unpredictable (especially around the Huntingdon and Cambridge area, and seems to be horrendous accidents, delays and tailbacks on this road several times a week and just makes travelling for a flight so unpredictable!
Stansted is practically ruled out for getting to via public transport, unless you are willing to make several connections.
Nearly everyone I know, including myself in the county considers Luton as our nearest and most convenient airport, followed by Birmingham. Simply because of the connections via the M1... I very rarely hear people saying they are flying from STN.
Public transport wise, Northampton has trains departing for Birmingham every 15 mins. Wellingborough, Kettering and Corby have direct half hourly intercity trains to Luton Airport Parkway which only takes 25 mins. BUT like Southend, early morning connections and late night arrivals are an issue, however both airports do have good connections with National Express to the county overnight.
I would even go as far to say Heathrow and Gatwick attract more traffic than Stansted from Northants with the better National Express links. Also just by changing platforms at Luton or Bedford, it is possible to get FCC trains to Gatwick.
As we are sort of up in the Midlands, Manchester Airport is a similar distance as Southend, of about 120 miles away!