Delayed delivery, UK order

I had a conversation with a Dell online rep concerning delivery timescales for an XPS15 laptop that I was about to order. The rep confirmed a delivery timescale with me, promising (I have an e-mail transcript of this) that the delivery would take place no later than 4 December 2013. The date is critical as I will be out of the country, and I need to take the laptop with me. Based on the information provided, I decided to go ahead and place the order (both conversation and order took place on 18 November). Dell's order processing system confirmed an expected delivery date of 2 December 2013, which suited my requirements. Today, I was sent an e-mail stating that the delivery date had been changed to 10 December, which is after my cutoff date. Interestingly, the online order status page still quotes 2 December, so I'm not really sure which one to believe. Now, I clearly can't delay my flight to wait for the laptop to turn up, so what other options are open to me? I phoned the customer support number, and spoke to someone who was only interested in quoting the terms and conditions of sale to me. This is not a helpful approach - especially since under  .  I'm not really interested in getting into a  match with Dell - all I want to do is to talk to someone who can tell me truthfully what is going on, and work with me to resolve the situation to my satisfaction.

I have a few additional questions:
1) Why did the sales agent make a false promise regarding delivery timescales?
2) What has caused the expected date to change, and why has it only just been brought to my attention?
3) When I spoke to someone today, they confirmed that shipping from the warehouse would take between 4 and 10 days - so why has it already taken longer than that to ship my order?
4) When attempting to e-mail the original agent's manager (as provided in the chat transcript), the message bounced back with an unknown address error. Why does this agent have out of date information in their footer?
5) Given that your stock management system was aware of current orders and stock levels, how is it possible to underestimate delivery timescales by so much?
6) Is Dell giving preferential treatment to 'more important' customers?

I am very disappointed with my experiences so far - Dell is supposed to be a reputable, trusted brand, and as such, you really should have a customer care operation to match. We all understand that things go wrong occasionally, but how you deal with that situation is what really matters. I need to talk to someone who can help me find a solution, rather than just sticking to a script. Come on Dell - your customers deserve better treatment.