That situation is crap, and I'm sorry to hear it.
To my knowledge, forced marriage is illegal in the UK and is considered domestic abuse - and rightly so.
Do you think that they're serious about kicking you out? Have you asked your parents why they are being hypocritical towards you, considering your dad is not Sikh?
I would say under no circumstance should you accept this, I understand you're very much caught between a rock and a hard place, but agreeing to marry someone you don't know, who you've only seen a picture of, and you're not attracted to?! This is your life, and any marriage ought to be on your terms and not something with the likelihood of making you miserable for the foreseeable future.