i have a appointment/assessment at the institute of contemporary music performance in london just wondering what do you think they will ask me to do and what should i play if they were to ask to me to play something?

better shred than dead
Have you asked them? If not - ring up and ask. The worst they can do is not tell you, and they'll probably appreciate you being pro-active.
Do a Jazz standard or something. Something that will show off your; rhythm, articulation, phrasing, dynamics, and improv.

One thing people on here hardly ever talk about is that you also have to enjoy playing the song. It comes through loud and clear if you hate it.