I am a student right now at an American university and I wish to work in London as soon as I graduate. Would I still be hired with an American degree or do UK employers prefer to get British students with UK degrees?

Yes they do.

In order to get the equivalent of your college degree in UK standard for employers to be able to decide on your application you need to contact UK Naric.

The service is accepted in the UK for study as well.

Link : http://www.naric.org.uk/