If not at half take-off speed by 1/3 of runway length start worrying. If not airborne by 2/3 runway length, abort.
Always assume that anybody flying a Piper or Cessna can't see you.
Never assume that you'll be given anything better than a FIS, no matter how much you beg.
Any aircraft designed in the USA will need the wing re-inforcing for UK approval.
Any aircraft designed in France will need the flying controls strengthening before UK approval.
Any aircraft designed in Germany will need to lose about 30kg before UK approval.
Any military customer will move the goalposts at least once every 2 months before completion of the project.
G