How to complain to Dell UK?

Hello all,

I need some info on where to send an official letter of complaint to Dell for their appalling customer services. I won't go into too much detail here as the issue has been going for 3 months, but the short version is..

I ordered a Dell inspiron back in December, which was faulty upon delivery (problem with the graphics card) I called customer services and they called me back within several days offering me to upgrade to a Dell Alienware M17 for a price, which I did. So far so good, however I had to make several calls for Dell to pick up the Inspiron, rather than they contact me, so I waited in. 3 weeks later the alienware turned up. Fantastic I thought, however this laptop turned up faulty too. It wouldn't charge, the keyboard lights wouldn't work correctly and a plastic base on the bottom of the laptop was already broke! I got passed from department to department from the inspiron department to the Alienware department to customer services to the technical department etc trying to resolve this issue but each department was unaware of the exchange that took place and couldn't help. So I reached out to Dell on Twitter, they agreed to replace it, so once again I waited several weeks for it be 'made' I got a delivery date, so another day off work and waited in, the delivery van turned up as expected but didn't take the faulty Alienware with him, but he nonetheless dropped off a Dell Inspiron! :| I reached out to Dell on twitter again who now have to get a quote for the replacement Alienware and want me to wait in again for the Inspiron to be picked up! I've taken several pictures and detailed all my calls/twitter so i wish to send them to someone as you really couldn't make this up. I'm several hundred pounds down, and I've had no working laptop for 3 months and have waited in at least 4 times for a delivery/collection and I'm at a total loss. The best bit? Apparently I'm no longer allowed a refund as my 'grace period' has been and gone. Any address/name/e-mail would be more then appreciated. 

Kind regards

Tyler,