Any organisation in London that would be willing to show us funtionalities of CiviCRM ?
Pleased to hear that you want to promote CiviCRM! 

This may not be the best place to ask this question.  You may have better luck on the CiviCRM chat site.

Alternatively you could search for a CiviCRM partner based in London and ask if they can help.

You may also be interested in the CiviCRM meetup in London.

Of course there are also the demo sites if you want to try it out for yourself.

I hope that helps.  Good luck!