Can we lower our offer on the house were buying now the market's dropped?

we're 1st time buyers in the uk and put in an offer for a property which was accepted feb 08. Since the offer was accepted we had trouble getting a mortgage but have now finally got one sorted and everything is ready for us to sign and complete. Over the past few months, while weve been getting things sorted, the housing market has dropped, so can we now go back to the estate agents to tell the vendor that we've been advised (by practically everybody) to rethink our offer and were not prepared to pay as much as we initially offered? I m in turmoil as i've never bought a house before, does anybody have any advice please?

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