CEN (the European Standards Organisation, has published a Corrigendum to EN 81-20. Corrigenda are used to issue corrections to EN standards after publication. BSI have now published this corrigendum in November 2015.
The error being corrected is in the note of clause 5.4.6.1 to change "0.70 cm" to "0.70 m". We do not believe that such a simple and obvious error is worth the re-purchase of a copy of BS EN81-20. If you have a copy of BS EN 81-20:2014, you can either correct it by hand or BSI have said that they will provide the Corrigendum free to replace previously purchased copies.
The content of the clause and note in the Corrigendum copy is as follows.
5.4.6.1 Where an emergency trap door is fitted to the car roof (see 0.4.2), it shall have minimum clear opening dimensions of 0,40 m × 0,50 m.
NOTE When space allows a trap door of 0,50 m x 0,70 m is preferable.