In article ,
(DFN) wrote:

We are looking into a flight into Heathrow and taking another flight
out one
of London's three other airports. We aren't certain which one we will be
using, it will depend on distance and time it would take to reach it.
How far are the airports from Heathrow?

As the crow (or 777) flies, Gatwick is the closest, Luton is a little
further and Stansted is by far the furthest.

But public transport costs aren't directly proportional to distance in the
UK (unlike countries where trains are charged per kilometre, for example),
so it may still be cheaper to go from an airport other than Gatwick,
depending on the airfares. And you may decide a slightly longer
interchange is worth the saving...

Incidentally, London actually has a fifth airport too, London City,
located in the east of the city itself. It's focused on short-hop business
travel, though.

Is there bus or train connection to them?
Do they accommodating with luggage?

You mean can you take luggage on buses/trains? Yes, effectively as much as
you want. (Though if your journey involves the London Underground be aware
this is very difficult with trolley-loads of luggage. You can always take
a taxi just to cross London if necessary and use trains or buses for the
rest of the trip.)

How much does it cost?
Are there any non-stop modes of transportation (other than taxis)?

Buses will be cheapest, taxis most expensive (unless you can cram the taxi
with people, perhaps), trains in the middle. If you decide to take a taxi
it's likely to be cheaper to book in advance.

Check http://www.gobycoach.com and http://thetrainline.com for details of
bus and train services respectively, because stops, timings and costs can
vary according to the day and the time of day.

Are the buses affected substantially by traffic?

They can be, but trains are also subject to delays sometimes and obviously
taxis are affected by traffic, so on its own it's not a big anti-bus
factor!