OK, so you are there 3m only. I assume you have a 6m Assured Shorthold Tenancy agreement?
The tenant is obligated to continue to the end of that agreement regardless, that 6m is guaranteed, you could be sued, for example if you left, and tried to give notice.
If I were you, I'd get a prospective tenant/flat mate lined up, explain the situation to them, and then go and talk to the LL/Agent.
SO.... if the agent/landlord is sensible, you can talk to them and say this is what has happened, but that you have this person lined up to share with you and help you meet the rent, and that could they give you both a trial until the end of the AST. Providing they are happy, a new contract could be given to you/lodger.
In the meantime, bone up on the rights of a lodger and if the 72hour notice is applicable, make sure the agent/LL knows you can terminate this at anytime. Tell the agent that in any event, you have savings to get you through the next 3m, so the rental is assured.
The 3m will give you ALL a chance to see if this will work, and minimise risk for all of you.
If you are only working part time, you may qualify for housing benefit. Get some CAB advice.