If that is all you can afford, then I would make it clear to the Agent that it is your final offer. Otherwise they will pester you trying to push you up to a higher figure especially if they think it is a speculative offer.
Go for it, its only a phone call and the worse that can happen is that they say no.
I am looking to buy a property i am a first time buyer the house that i have seen is a new build it was completed in 2010 its still on the market on at £230 it is a 3 bed detached way over priced. The builder has removed it from one agent and put it for sale by another agent. As it is new build a 15% deposit is needed. Its been on the market 2-3 years could i offer in the region of £160 or is this way to low any advice is apreciated.