Sam
A 714 is a card you will need if sub-contracting to a construction company, you present the card to the firm, and they are then able to deduct tax @18 % from gross payments due to you.
If you apply at your local tax office, you should receive it in a couple of weeks, so get down there tomorrow!
Do not give up on that job because of the window cleaning, check to see if windows are 'tilt and turn' so that they might be done safely,from the inside, or ask if it is possible to clean them before the scaffold comes down ?
Regards.........Jake