Re: whats allowed in hand luggage...anything under 100ml?
Nadz, clip-in extensions might set off the metal detectors depending on how sensitive they're turned up (bear in mind summer holidays could mean higher security levels). If ur really unlucky u may get asked to take them out, if it bothers u and u absolutely want to wear them during the flight u can always get rid of the clips and just use adhesive instead.
I know a girl who was asked to take out the pins in her hijab cos they were setting off the alarm and she had to do it there and then.