The best way of checking the notes is by comparing to a legitimate £20 note.   Pay particular attention to the following;

*Window bottom right hand corner should have 20's in it

*Hologram bottom left should say ‘Twenty' and ’Pounds' when tilted  

*'Bank of England' on front of note should be in raised print

*Braille down top left hand side of note should be : :

                                                                                 : :

                                                                                 : :

*You shouldn't be able to scratch any of the print off

*Compare colouring and ‘sound’ when note is scrunched up (the fake notes sound different)