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I totally sympathise with your situation, but legally, I'm afraid there is nothing you can do just yet to push them for a completion date or indeed request any compensation from them.
Under new Build Contracts, all Developers need to stipulate an "Estimated Build date", which I am guessing would have been sometime in July. Under the terms of the Contract, both parties are legally bound to complete as and when the property is ready, with th eadditional proviso that a Buyer can pull out and terminate the Contract if the new Build is not ready six months after the Estimated Build date (ie probably Jan 2015 sometime.
Until this 6 month period has elapsed, the Builder can legally take as little or long time to build th eproperty, safe in the knowledge that there is absolutely nothing the Buyer can do about this.
I would expect more from Taylor WImpey, but I'm afraid your hoands are tied until the 6 month period has expired. If i were you, I would still write to them formally, expressing your frustration, and highlighting the possible financial implications to you of the delay. They may offer you some compensation as a gesture of goodwill, but please don't bank on it.
I am sorry this is not the answer you were looking for, but it sets out the legal position.