According to section 3 of our
Aeronautics Act, R.S.C. 1985, c.A-2
"aerodrome" means any area of land, water (including the frozen surface thereof) or other supporting surface used, designed, prepared, equipped or set apart for use either in whole or in part for the arrival, departure, movement or servicing of aircraft and includes any buildings, installations and equipment situated thereon or associated therewith ...
"airport" means an aerodrome in respect of which a Canadian aviation document is in force.
In other words, virtually anything (including a farmer's field, etc.) can be an "aerodrome", so long as it is used by aircraft; whereas an "airport" is essentially a licensed aerodrome, and as such has to meet certain guidelines under Part III of the
Canadian Aviation Regulations. I imagine that roughly similar provisions apply in the UK (see the definition of "aerodrome" in
CAP 168); but don't take my word for it, ask Aerodrome Standards (
[email protected]).